The Measurement Properties and Factor Structure of

The Measurement Properties and Factor Structure of the Test of Visual-Perceptual Skills–Revised: Implications for Occupational Therapy Assessment and Practice G. Ted Brown, Isabelle Gaboury

OBJECTIVES. The aim of this study was to examine the measurement properties of the Test of VisualPerceptual Skills–Revised (TVPS–R).

METHODS. A group of 356 typically developing children 5–11 years of age completed the TVPS–R along with three criterion measures.

RESULTS. Several of the TVPS–R items had item–total subscale correlation coefficients were lower than the 0.20 correlation criteria. Cronbach’s alpha coefficients varied between 0.74 and 0.84 for the seven subscales. The perceptual quotient (PQ) reliability coefficient for the age levels ranged between 0.79 and 0.91. The PQ total group reliability coefficient was 0.96. Results from the principal component analysis indicated that the majority of the TVPS–R items loaded on a dominant first factor. Confirmatory factor analytic models were assessed using four different goodness-of-fit indices. Two of the fit indices supported the unidimensional assumption (RMR and CFI ), while two of the fit indices did not support the TVPS–R one-factor model (chi-square and RMSEA). A unitary motor-free visualperceptual factor was not found.

CONCLUSION. The TVPS–R PQ should not be used as an overall performance summary score. Of the seven TVPS–R subscales, five can be used with confidence (visual discrimination, visual-spatial relationships, visual-sequential memory, visual figure ground, and visual-closure) whereas the visual memory and visualsequential memory subscales are not recommended. Brown, G. T., & Gaboury, I. (2006). The measurement properties and factor structure of the Test of Visual-Perceptual Skills–Revised: Implications for occupational therapy assessment and practice. American Journal of Occupational Therapy, 60, 182–193.

Introduction

G. Ted Brown, PhD, MSc, MPA, BScOT(Hons), OT(C), OTR, AccOT, is Senior Lecturer, Occupational Therapy Program, School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University–Peninsula Campus, PO Box 527, Frankston, Victoria 3199, Australia; [email protected] Isabelle Gaboury, BSc, MSc, is Biostatistician, Chalmers Research Group, Children’s Hospital of Eastern Ontario Research Institute, Ottawa, Ontario, Canada and Doctoral Student, Population Health PhD Program, University of Ottawa, Ottawa, Ontario, Canada.

182

Occupational therapists often assess and treat visual-perceptual problems in school-age children and adolescents (Case-Smith, 2001; Gentile, 1997; Schneck, 1996; Wallen & Walker, 1995). Visual-perceptual dysfunction can have a negative impact on a number of occupational performance and functional skill areas for children including difficulties in reading, spelling, cursive and manuscript written output, visual-motor integration, mathematics, activities of daily living, participation in play/recreational/leisure activities, and completion of schoolrelated work (Bouska, Kauffman, & Marcus, 1990; Erhardt & Duckman, 1997; Reid & Drake, 1990; Schneck & Lemer, 1993; Weil & Amundson, 1994). Occupational therapists try to determine the possible causes and types of visualperceptual dysfunction both by administering standardized instruments and making informal observations (Chia, 1997). Therefore, it is important for occupational therapists to use visual-perceptual instruments that possess sound measurement properties (Asher, 1996; Chu & Hong, 1997; Plapinger & Sikora, 1995; Reid & Jutai, 1997). Measurement properties include reliability, validity, sensitivity to change, and clinical utility (Law, Baum, & Dunn, 2001). By using scales that have acceptable levels of reliability and validity, occupational therapists can then make informed decisions about which visual-perceptual tests are the most appropriate to use with March/April 2006, Volume 60, Number 2

children and adolescents. The problem is that currently, “there are few well-developed clinical assessment tools available that are designed to evaluate the visual perception aspects of vision” (Reid & Jutai, 1997, p. 82). The visualperceptual instruments most frequently used by pediatric occupational therapists include the Developmental Test of Visual-Motor Integration (VMI), Test of Visual Perception Skills–Revised (Non-Motor) (TVPS–R), Motor Free Visual Perception Test–Revised (MVPT–R), Test of Visual-Motor Skills–Revised (TVMS–R), Sensory Integration and Praxis Tests (SIPT), Developmental Test of Visual Perception–2 (DTVP–2), and Wide Range Assessment of Visual-Motor Abilities (WRAVMA) (Burtner, McMain, & Crowe, 2002; Chu & Hong, 1997; Crowe, 1989; Reid, 1987; Rodger, 1994; Schneck, 1996). It is important for occupational therapists to be aware of how the instruments and scales they use in their clinical practice were developed, the reliability scores obtained in the standardization process, the validation procedures used to create them, and any inherent weaknesses and limitations they might possess. In this paper, the measurement properties and factor structure of the TVPS–R (Bishop & Curtin, 2001; Burtner, McMain, & Crowe, 2002; Denison, 1985; Feder, Majnemer, & Synnes, 2000; Gardner, 1996; Hung, Fisher, & Cermak, 1987; McFall, Deitz, & Crowe, 1993; Miller, Missiuna, MacNab, Mallory-Miller, & Polatajko, 2001) will be presented and discussed. Initially, the psychometric properties reported in the TVPS–R manual will be reviewed. Then the reliability, criterion/convergent validity, and construct validity/factor structure of the TVPS–R will be discussed. The TVPS–R was chosen for further study even though there are a range of other visual-perceptual instru-

ments available. First, even with the 1982 edition being revised and updated in 1996, the reliability and validity properties of the TVPS–R have received limited attention in the peer-reviewed literature to date. Second, based on previous surveys of test use by pediatric occupational therapists, the TVPS–R was one of the top three most frequently used instruments. Finally, it is important to evaluate the construct validity of the TVPS–R so that clinicians making high-stakes decisions related to clients can do so with greater confidence.

Literature Review The TVPS–R evaluates seven visual-perceptual subskills: (a) visual discrimination (VD), (b) visual memory (VM), (c) visual-spatial relationships (VSR), (d) visual-form constancy (VFC), (e) visual-sequential memory (VSM), (f ) visual figure ground (VFG), and (g) visual-closure (VC) (Gardner, 1982; 1996). The definitions of the seven visual-perceptual subskills that the subscales evaluate are located in Table 1. There are 16 items on each of the seven subscales, which are arranged progressively according to their level of increasing difficulty. The subscale items consist of various geometric shapes and designs. The TVPS–R is designed for use with school-age children between 4 and 12 years of age. They respond by selecting the correct choice from a multiple-choice format that does not require motor responses such as drawing or copying shapes, which is why the TVPS–R is referred to as being motor-free or nonmotor. It takes approximately 30–45 min to administer the TVPS–R depending on the age of the child and 5–10 min to score. The child is shown the test plates and asked to point to the correct response from

Table 1. Definitions of the Test of Visual-Perceptual Skills–Revised Subscales Visual Perception

The capacity to interpret or give meaning to what is seen. It includes recognition, insight and interpretation at the higher levels of the central nervous system of what is seen

Visual Discrimination

The ability to match or determine exactly characteristics of two forms when one of the forms is among similar forms

Visual Memory

The ability to remember for immediate recall (after 4 or 5 seconds) all of the characteristics of a given form, and being able to find this form from an array of similar forms

Visual-Spatial Relationships

The ability to determine, from among five forms of identical configuration, the one single form or part of a single form that is going in a different direction from the other forms

Visual-Form Constancy

The ability to see a form, and being able to find that form, even though the form maybe smaller, larger, rotated, reversed and/or hidden

Visual-Sequential Memory

The ability to remember for immediate recall (after f4 or 5 seconds) a series of forms from among four separate series of forms

Visual Figure Ground

The ability to perceive a form visually, and to find this form hidden in a conglomerated ground of matter

Visual-Closure

The ability to determine, from among four incomplete forms, the one that is the same as the stimulus form (e.g., the completed form)

Source: Gardner, M. F. (1996). Test of Visual-Perceptual Skills (Non-Motor)–Revised. San Francisco: Psychological and Educational Publications.

The American Journal of Occupational Therapy

183

among four or five choices on the page. Scoring is accomplished by summing the correct number of responses on each subscale and then determining derived scores. The subscale items are scored dichotomously. In addition to raw scores, the TVPS–R manual includes a full range of commonly used derived scores. Various standardization scores, including standard scores, scaled scores, T scores, percentile ranks, and stanines can be derived to describe a child’s performance on the seven subscales. Sums of scaled scores and perceptual quotients (PQs) were developed to describe performance on the TVPS–R as a whole. A perceptual quotient represents a child’s overall visual-perceptual performance that incorporates the seven subtypes of visual perception as defined by the TVPS–R (Gardner, 1996). Perceptual age equivalents for each subscale are also available. By including scores for each subscale across eight age groups (4–12 years of age), (such as standard scores for total performance [described as PQs], percentile ranks, and perceptual ages), clinicians can use several methods for interpreting a child’s score. A detailed review and critique of the TVPS–R is included in Brown, Rodger, and Davis (2003). Gardner (1996) presented several types of reliability information in the TVPS–R manual. Reliability coefficients and the standard error of measurement provide estimates of the consistency or precision of an instrument. The internal consistency formula for dichotomous data, KD–20, was used to evaluate the reliability of the TVPS–R subscales. Total score reliabilities were calculated using a formula for the reliability of the composite scores. The reliability coefficients for the total score ranged from 0.83 to 0.91. The median reliability coefficients across all age levels ranged from 0.42 to 0.61, and the total group reliability coefficients ranged from 0.74 to 0.85 (Gardner, 1996). Reliabilities for individual subscales ranged from 0.27 to 0.80 (Gardner, 1996). Gardner (1996) reported that item-total correlations by subscale varied: VD (0.24–0.53), VM (0.08–0.51), VSR (0.31–0.65), VFC (0.18–0.55), VSM (0.27–0.57), VFG (0.28–0.48), and VC (0.21–0.60). When reviewing items included in the TVPS–R, just one of the seven items identified as showing low item-total correlation values only was removed from the original version during the revision. These findings suggest that the measurement properties of the revised version of the Test of Visual-Perceptual Skills (TVPS) would likely be strengthened if items exhibiting low item-total correlations (e.g., < 0.20) were amended. Three types of validity are reported in the TVPS–R manual: content validity, criterion-related validity, and construct validity. Content validity was exhibited by the 184

fact that (a) only those items that met all inclusion criteria with respect to item-total correlations and internal consistency were retained in the final form of the test, (b) none of the items that exhibited a potential gender bias were included, and (c) the items that were selected represented varying levels of difficulty suitable for measuring a wide range of visual-perceptual skills across the age levels of interest (Gardner, 1996). Content validity was determined by analyzing items by level of difficulty and by their relationship to the subscale score value and the total score value. Only those items that correlated with both the subscale and total scaled score and showed a stronger correlation with its subscale than the other subscales were included. Items were arranged in the test booklet by ascending order of difficulty. Two aspects of criterion-related validity were reported. In the first instance, information concerning the concurrent validity was obtained by correlating the standard scores from the TVPS–R to standard scores from seven other instruments, including the subscales of: (a) the Test of Visual-Motor Skills–Revised, (b) the Test of AuditoryPerceptual Skills–Revised, (c) the Test of Nonverbal Intelligence, (d) the Test of Academic Achievement Skills (reading and arithmetic subtests), (e) the Wechsler Preschool and Primary Scale of Intelligence–Revised (vocabulary and picture completion subscales), (f ) the Weschler Intelligence Scale for Children–Third Edition (vocabulary and picture completion subtests), and (g) Wide Range Achievement Test–Third Edition (reading subscale). These seven instruments were administered concurrently with the TVPS–R as part of the 1996 standardization and revision process. Correlation coefficients ranged from 0.12 to 0.45 between the TVPS–R and the criterion variables. Gardner, the test developer, concluded that these correlations were in the low to moderate range. He claimed that these correlations indicated that the TVPS–R was measuring specific visual-perceptual skills rather than overall intellectual functioning. However, no specific information discussing the criterion variables chosen and the expected relationship between the TVPS–R and the criterion variables was reported in the test manual. There have been few studies published in the referenced literature about the TVPS or the TVPS–R. Only one study examined the construct validity/factor structure of the TVPS (Klein, Sollereder, & Gierl, 2002) and none to date have evaluated the TVPS–R. Based on the information available, the following research questions were posed. First, what are the point-biserial correlations between each TVPS–R item and its subscale? Second, what is the internal consistency of the seven TVPS–R subcales? Third, what is March/April 2006, Volume 60, Number 2

the relationship between the TVPS–R PQ and subscale standard scores with the visual-perceptual criterion variables? Finally, what is the latent factorial structure of the seven TVPS–R subscales and overall TVPS–R combined scale? Answering these research questions will contribute valuable evidence about the conceptual consistency of the seven TVPS–R subscales as well as the TVPS–R’s ability to measure the overall construct of visual perception.

Method Design The design was a prospective cross-sectional evaluation that examined the measurement properties of the TVPS–R. Sample Children who were enrolled in each of the grade levels of junior kindergarten and grades one through six were recruited to participate in the study. The children were recruited from informal networks known to the first author as well as from two private schools and one publicly funded Catholic school in the Ottawa-Carleton area, Ontario, Canada. Boys and girls were eligible for this study if: (a) consent to participate in the study (by both the child and their parent or guardian) was obtained, (b) the child was between 5 and 11 years old, (c) the child had proficient English speaking and listening skills, and (d) the child had an absence of any major diagnosed intellectual or physical impairment(s). Ethics committee approval from the University of Queensland Behavioural and Social Sciences Ethical Review Committee, Brisbane, Queensland, Australia, and from the Children’s Hospital of Eastern Ontario Ethical Review Committee was obtained before the data collection was initiated. Instrumentation A screening questionnaire was used first to determine which children met the study inclusion criteria. A demographic questionnaire was used to gather relevant background data about the children. The TVPS–R was then administered to 356 children. The children also completed three other tests of motor-free visual perception (used as criterion validity variables) in the same time period when they answered the TVPS–R. These were the visual perception subscale of the Developmental Test of Visual-Motor Integration (VMI; Beery, 1997), the Motor-Free Visual Perception Test– Revised (MVPT–R; Colarusso & Hammill, 1996), and the four motor-free visual-perceptual subscales of Developmental Test of Visual Perception–2 (DTVP–2; Hammill, Pearson, & Voress, 1993). The American Journal of Occupational Therapy

Data Analysis The Statistical Package for the Social Sciences Version 10.0 was used for the data entry, its storage and retrieval, and data analysis. Descriptive statistics were calculated for all TVPS–R variables. Point-biserial correlations were generated to examine the relationship of each TVPS–R item to its subscale. Alpha coefficients were calculated for the total group and by age for each subscale to determine internal consistency of the TVPS–R. Criterion/convergent validity was examined by computing Pearson product moment correlations between the TVPS–R PQ and subscale standard scores with criterion variables. The criterion variables included the VMI, MVPT–R, and the DTVP–2 subscales. To evaluate the latent (unobserveable) structure of the seven TVPS–R subscales, two analyses were completed. The purpose was to determine if the TVPS–R subscale items loaded on the same factor (in this case motor-free visual perception). First, an exploratory factor analysis using the tetrachoric correlation matrix for the full sample was computed using principal axis factor extraction. Tetrachoric correlations were used because the item responses were scored dichotomously. The seven TVPS–R subscales were analyzed separately so the factor loadings for each individual subscale could be examined. Factor loading is another way to express the correlation between an item and its subscale. If a unidimensional factor adequately described each subscale, the factor loadings for the observed construct or subconstruct would be large (e.g., > 0.35). A confirmatory factor analysis (CFA) was conducted using EQS 5.7b (a data analysis software program). A similar CFA methodology was completed by Klein et al. (2002) on data from a group of children with known learning disabilities from the 1982 version of the TVPS. The indicators were created by summing the children’s responses across each of the 16 items to create a subscale score. Only the one-factor model was assessed because the developer of the TVPS–R assumed that it is unidimensional, thereby allowing the subscale scores to be added together to generate a fullscale score (known as a PQ). This assumption is evaluated by fitting the seven TVPS–R subscales to a one-factor model. CFA models are assessed using goodness-of-fit indices. Four types of fit indices were used to assess each model because there is little agreement amongst researchers as to which model provides the best measure of fit (Bollen & Long, 1993). The first index is the chi-square statistic. Chi-square is used to determine if the restrictive hypothesis tested can be rejected. A model is considered to have acceptable fit if the difference between the variance–covariance matrix generated 185

by the original data and by the hypothesized solution is small, yielding a nonsignificant chi-square. In other words, a model is said to have a good fit if p is nonsignificant (Anastasi & Urbina, 1997). The second index is the root mean square error of approximation (RMSEA). The RMSEA is meant to provide a measure of parsimony by assessing the discrepancy per degree of freedom in the model. The RMSEA takes into account the number of free parameters required to achieve a given level of fit. Browne and Cudek (1993) suggest that an RMSEA of 0.05 indicates a close fit of the model in relation to degrees of freedom. They also state that an RMSEA value of 0.08 or less would indicate a reasonable error of approximation, and would not use a model with an RMSEA greater than 0.1. The third index is the root mean square residual (RMR). RMR represents an average of the absolute discrepancies between the observed covariances fitted and the hypothesized covariances. A small RMR indicates good model fit (Nunnelly & Bernstein, 1994). The fourth index is the comparative fit index (CFI; Bentler, 1990). This index is a revised version of an earlier normed fit index by Bentler and Bonett (1980), and it adjusts for degrees of freedom. The chi-square value of the estimated model is compared to the chi-square value of a “null” model. This null model assumes that all the observed variables are independent, and the covariance between variables is disregarded. Values range from 0 (poor fit) to 1 (good fit) and values above 0.90 are considered acceptable. Procedures Data collection took place in the homes of the children or at their schools during nonscheduled classroom teaching times. Parents or guardians were required to sign a consent form in order for their child to participate in the study. The TVPS–R was administered by four occupational therapists, each of whom had 4 or more years of pediatric experience. Data-entry validation procedures were completed to ensure accuracy and reliability of the data.

16.3%, grade four, 15.7%, grade five, 9.3%, grade six, 8.4%, and grade seven, 2.5%. Half of the subjects were enrolled in the public school system (n = 178), 26.7% were enrolled in the Catholic school system (n = 95), and the remainder were enrolled in the private school system (23.3%). In Ontario both the public school system and the Catholic school system are funded by the provincial government. The majority of the subjects spoke only English (71.3%), whereas the rest spoke English and French (25.6%), English and another language (1.7%), or English, French, and another language (1.4%). A Pearson chi-square test indicates no statistical difference in gender distribution across age level (p = 0.995). Data were not gathered about race or ethnicity of the children due to human ethics committee objections. The sample size was deemed large enough to complete the CFA (Kim & Mueller, 1978; Long, 1983). The sample size was also adequate to provide the necessary power to complete the data analyses with confidence (Cohen, 1988; Norman & Streiner, 1994). Test of Visual-Perceptual Skills–Revised Item Analysis Results Means and standard deviations for the TVPS–R PQ score, subscale raw score values, and subscale standard score values are reported in Table 2. Each subscale has values from 0 (child answers all of the subscale items wrong) to 16 (child answers all the subscale items correctly). According to the TVPS–R manual instructions, if a child answers three out of five items incorrectly, then the child moves on to the next subscale without answering the rest of the items on that particular subscale. It was noted that the standard deviations of the participants in this study were much larger than the ones reported in the TVPS–R manual. Potential reasons for this factor were that children were not randomly selected and that children were recruited from a variety of school settings, which in turn could have impacted on their performance scores. Subscale raw scores ranged from 9.9 (SD = 4.6) to 13.4 (SD = 3.5) and subscale standard score values ranged from

Results

Table 2. Perceptual Quotient and Subscale Standard Scores of the Test of Visual-Perceptual Skills–Revised

Demographic Data Related to Subjects

Variable (M, SD )

In all, 356 children ranging from 5 to 11 years of age were recruited for this study; of those, 171 or 48% were boys and 185 or 52% were girls. The children came from junior kindergarten through to grade seven. The total sample percentage distribution of children in each grade level was as follows: junior kindergarten, 3.1%, senior kindergarten, 14.9%, grade one, 16%, grade two, 13.8%, grade three, 186

TVPS–R PQ Visual discrimination Visual memory Visual-spatial relations Visual-form constancy Visual-sequential memory Visual figure group Visual-closure

Raw Mean Score 12.4 11.7 13.4 11.2 9.9 12.1 10.3

(3.7) (3.3) (3.5) (3.8) (4.6) (3.9) (4.7)

Standard Score 113.4 107.8 101.5 112.5 106.1 100.4 114.0 101.9

(27.8) (18.2) (21.1) (13.7) (18.0) (21.4) (17.7) (20.4)

Note. PQ = perceptual quotient; TVPS–R = Test of Visual-Perceptual Skill–Revised.

March/April 2006, Volume 60, Number 2

Table 3. Item Analysis–Correlation Values Between Each Test of Visual-Perceptual–Revised Item and Its Subscale Score Item

VD

VM

VSR

VFC

VSM

VFG

VC

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

.26 .51 .61 .53 .51 .48 .35 .59 .55 .69 .60 .41 .53 .53 .59 .48

.19 .49 .48 .38 .50 .38 .53 .52 .23 .56 .63 .29 .50 .48 .50 .35

.38 .28 .45 .51 .56 .58 .59 .58 .50 .72 .49 .57 .57 .57 .55 .52

.01 .27 .37 .51 .53 .50 .59 .37 .52 .56 .54 .38 .35 .51 .47 .38

.37 .51 .45 .48 .43 .51 .53 .45 .52 .47 .40 .57 .38 .45 .24 .44

.25 .36 .39 .34 .52 .55 .58 .28 .58 .53 .37 .38 .41 .51 .50 .57

.22 .40 .55 .59 .57 .34 .48 .63 .51 .62 .55 .71 .50 .48 .64 .44

Note. TVPS–R PQ = Test of Visual-Perceptual Skills–Revised perceptual quotient. Subscales: VD = visual discrimination; VM = visual memory; VSR = visual-spatial relations; VFC = visual-form constancy; VSM = visual-sequential memory; VFG = visual figure ground; VC = visual-closure.

a mean of 100.4 (SD = 21.4) to 112.5 (SD = 13.7). Table 3 presents total subscale score correlation values between each item and its subscale score. Correlation values for each subscale varied: VD (.26–.69), VM (.19–.63), VSR (.28–.72), VFC (.01–.59), VSM (.24–.57), VFG (.25–.58), and VC (.22–.71). It has been reported that items with correlations less than .20 should be excluded from a scale (Anastasi & Urbina, 1997; Kline, 1986). Based on the correlation analysis results, several TVPS–R subscale items should potentially be removed from their subscale. In other words, TVPS–R subscale items VM 1, VFC 1, VSM 15, and VC 1 failed to meet the psychometric inclusion criterion. Internal Consistency Alpha coefficients are reported by age for the TVPS–R subscale scores and PQ score (Table 4). For acceptable subscale internal consistency reliability, alpha coefficients should be above 0.70 (Streiner & Norman, 1996); although some Table 4. Reliability Coefficients by Age for Test of Visual-Perceptual Skills–Revised Subscale Scores

authors argue that a value of 0.80 should be used (Kline, 1986). Based on individual age groups by subscale, internal consistency reliability coefficients varied: VD (0.44–0.75), VM (0.18–0.65), VSR (–0.01–0.79), VFC (0.54–0.67), VSM (0.37–0.76), VFG (0.42–0.67), and VC (0.33–0.73). Reliability coefficients by subscale for the total group varied between 0.74 and 0.84. The TVPS–R PQ reliability coefficient for the seven age levels ranged between 0.79 and 0.91. The TVPS–R PQ total group reliability coefficient was 0.96. All total group subscales exhibited acceptable reliability. However, none of the TVPS–R subscales demonstrated acceptable internal consistency reliability (alpha coefficient of 0.70 or higher) through all of the age levels. The correlation relationship between the TVPS–R PQ and subscale scores are presented in Table 5. It is reported that correlation values between .00 and .25 exhibit little if any relationship; values between .26 and .49 show a low relationship; values between .50 and .69 a moderate relationship; and values .70 and above a high relationship (Kline, 1986). The VM, VSR, and VSM subscales demonstrate a low relationship to the TVPS–R PQ score. The VFC and VFG both exhibit a moderate relationship with the TVPS–R PQ. The VD subscale demonstrates a high relationship with the TVPS–R PQ score. The intersubscale correlations are lower, ranging from .30 to .54. Using the above mentioned cut-off points, it is noted that this data set presents low to high correlations between the TVPS–R PQ and its subscales. It is interesting to note that the two subscales that involve a memory component (VM and VSM) present with the lowest correlation to the TVPS–R PQ. Criterion/Convergent Validity The means and standard deviations of the scales of the VMI, MVPT–R, and DTVP–2 are located in Table 6. Intercorrelations between the TVPS–R PQ score, TVPS–R subscale standard scores, and criterion variables (VMI, MVPT–R, and DTVP–2) are located in Table 7. Using the Table 5. Intercorrelations Between the Test of Visual-Perceptual Skills–Revised Perceptual Quotient and the Subscale Standard Scores

Age

N

VD

VM

VSR

VFC

VSM

VFG

VC

PQ

5 6 7 8 9 10 11

57 56 56 57 55 36 39

.75 .74 .64 .44 .75 .74 .45

.65 .61 .61 .49 .18 .36 .57

.79 .74 .70 .54 .32 .39 -.01

.56 .66 .56 .67 .54 .56 .54

.52 .76 .64 .56 .37 .45 .52

.59 .67 .59 .43 .51 .70 .42

.63 .67 .70 .72 .73 .62 .33

.91 .93 .90 .88 .84 .88 .79

Item

VD

VM

VSR

VFC

VSM

VFG

VC

TVPS–R PQ VD VM VSR VFC VSM VFG

.71*

.44* .39*

.46* .54* .48*

.50* .42* .35* .38*

.45* .35* .38* .32* .30*

.50* .45* .38* .46* .40* .31*

.53* .47* .41* .41* .53* .33* .46*

356

.82

.74

.83

.75

.78

.77

.84

.96

*All coefficients are significant at the 0.01 level.

Total group

Note. TVPS–R PQ = Test of Visual-Perceptual Skills–Revised perceptual quotient. Subscales: VD = visual discrimination; VM = visual memory; VSR = visual-spatial relations; VFC = visual-form constancy; VSM = visual-sequential memory; VFG = visual figure ground; VC = visual-closure.

The American Journal of Occupational Therapy

Note. TVPS–R PQ = Test of Visual-Perceptual Skills–Revised perceptual quotient. Subscales: VD = visual discrimination; VM = visual memory; VSR = visual-spatial relations; VFC = visual-form constancy; VSM = visual-sequential memory; VFG = visual figure ground; VC = visual-closure.

187

Table 6. Means (M ) and Standard Deviations (SDs) of the Three Visual-Perceptual Criterion Measures Variable (M, SD )

M (SD )

VMI MVPT–R total MVPT–R I MVPT–R II MVPT–R III MVPT–R IV MVPT–R V DTVP–2 I DTVP–2 II DTVP–2 III DTVP–2 IV DTVP–2 visual-perceptual quotient

113.1 (16.7) 33.1 (5.4) 7.5 (0.9) 4.6 (0.8) 6.2 (1.1) 10.2 (2.7) 4.6 (1.1) 10.8 (2.6) 11.7 (2.9) 10.5 (3.9) 13.2 (2.2) 110.2 (13.4)

Note. TVPS–R = Test of Visual-Perceptual Skills–Revised; VMI = Developmental Test of Visual-Motor Integration; MVPT–R = Motor-Free Visual Perception Test; DTVP–2 = Developmental Test of Visual Perception–2; MVPT–R I = visual discrimination; MVPT–R II = visual figure ground; MVPT–R III = visual-closure; MVPT–R IV = visual-form constancy; MVPT–R V= visual-spatial relationships; DTVP–2 I = position in space; DTVP–2 II = figure ground; DTVP–2 III = visual-closure; and DTVP–2 IV = form constancy; and DTVP–2 PQ = DTVP–2 visual-perceptual quotient.

same levels of correlation cut-off points as above, it is evident that the TVPS–R subscales presented weak criterion validity compared to other visual-perceptual instruments that supposedly measure the same construct. The TVPS–R PQ showed a higher moderate relationship with the MVPT–R total scale score and DTVP–2 visual-perceptual quotient. The TVPS–R PQ exhibited a low correlation relationship with the VMI, the five MVPT–R subscales, and the four DTVP–2 subscales. Similarly, the TVPS–R subscales all exhibit a low relationship with the VMI, the five MVPT–R subscales, and the four DTVP–2 motor-free visual-perceptual subscales. Only the TVPS–R Table 7. Intercorrelations Between the Test of Visual-Perceptual Skills–Revised, the Subscale Standard Scores, and Criterion Variables

VC subscale exhibits a moderate relationship with the MVPT–R subscale total score, MVPT–R IV subscale, and DTVP–2 III motor-free visual-perceptual subscale. The overall TVPS–R scores are only moderately valid when compared to other instruments that claim to be measuring the same or related theoretical construct(s). Latent Factor Structure From Exploratory Analysis Results from the principal component analysis indicate that the majority of the test items across the seven TVPS–R subscales load on a dominant first factor. The structure loadings for the first factor on each of the seven TVPS–R subscales are shown in Table 8. Using the factor loading cut-off of 0.35, it is apparent that only the items of the VD (0.45–0.92), VSR (0.59–0.94), VSM (0.35–0.82), VFG (0.38–0.90), and VC (0.44–0.90) subscales all load consistently on the first factor. Only 14 of the 16 items load on the first factor for the VM (0.22–0.80) and VFC (-0.72–0.88) subscales. These results present a mixed picture for the subscale factor structure of the TVPS–R with the items for some scales (e.g., VD, VSR, VSM, VFG, and VC) consistently loading on the first dominant factor whereas items for other subscales (e.g., VM and VFC) appear to be multidimensional (which is undesirable). Based on this analysis, it is unclear whether the same visualperceptual factor is being measured consistently by the seven TVPS–R subscales. Latent Factor Structure From Confirmatory Analysis A confirmatory analysis was used to evaluate the factor structure for all seven TVPS–R subscales simultaneously by

Table 8. Exploratory Factor Analysis of Test of Visual-Perceptual Skills–Revised: Structure Loading by Subscale

Variable

PQ

VD

VM

VSR

VFC

VSM

VFG

VC

Item

VD

VM

VSR

VMI MVPT–R total MVPT–R I MVPT–R II MVPT–R III MVPT–R IV MVPT–R V DTVP–2 I DTVP–2 II DTVP–2 III DTVP–2 IV DTVP–2 quotient

.33 .51 .37 .39 .35 .48 .38 .39 .24 .44 .40 .54

.34 .49 .39 .40 .33 .45 .35 .43 .21 .40 .35 .50

.32 .39 .29 .26 .23 .39 .27 .42 .25 .31 .34 .47

.36 .49 .35 .44 .37 .42 .41 .43 .16 .35 .32 .45

.41 .48 .33 .39 .29 .44 .41 .33 .30 .42 .49 .55

.25 .36 .27 .31 .29 .30 .29 .30 .17 .30 .27 .38

.37 .40 .30 .33 .26 .38 .30 .33 .27 .41 .44 .52

.41 .55 .33 .39 .31 .56 .42 .42 .32 .54 .46 .64

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

.70 .78 .92 .68 .80 .65 .48 .81 .66 .81 .75 .45 .67 .68 .82 .60

.67 .69 .77 .56 .46 .38 .73 .66 .22 .77 .80 .26 .59 .59 .62 .46

.78 .72 .90 .78 .72 .75 .75 .86 .70 .94 .59 .74 .88 .70 .72 .60

Note. TVPS–R = Test of Visual-Perceptual Skills–Revised; VMI = Developmental Test of Visual-Motor Integration; MVPT–R = Motor-Free Visual Perception Test; DTVP–2 = Developmental Test of Visual Perception–2; MVPT–R I = visual discrimination; MVPT–R II = visual figure ground; MVPT–R III = visual-closure; MVPT–R IV = visual-form constancy; MVPT–R V = visual-spatial relationships; DTVP–2 I = position in space; DTVP–2 II = figure ground; DTVP–2 III = visual-closure; and DTVP–2 IV = form constancy; and DTVP–2 PQ = DTVP–2 visual-perceptual quotient.

188

VFC –.72 .70 .80 .71 .88 .47 .59 .30 .74 .55 .62 .39 .36 .55 .55 .56

VSM

VFG

VC

.68 .76 .45 .65 .65 .50 .73 .49 .72 .54 .65 .82 .49 .60 .35 .61

.90 .76 .60 .75 .73 .63 .73 .99 .64 .68 .38 .68 .64 .84 .54 .78

.68 .66 .79 .80 .80 .44 .54 .65 .63 .72 .66 .90 .73 .58 .84 .60

Note. TVPS–R = Test of Visual-Perceptual Skills–Revised. Subscales: VD = visual discrimination; VM = visual memory; VSR = visual-spatial relations; VFC = visual-form constancy; VSM = visual-sequential memory; VFG = visual figure ground; VC = visual-closure.

March/April 2006, Volume 60, Number 2

Table 9. Fit Indices for the Test of Visual-Perceptual Skills–Revised One-Factor Model Model Chi-square RMSEA RMR CFI

35.06 (df = 14) 0.065* 0.177 0.990*

*Coefficients are significant at the 0.01 level. Note. TVPS–R = Test of Visual-Perceptual Skills–Revised; RMSEA = root mean square error of approximation; RMR = root mean square residual; CFI = comparative fit index.

fitting the subscale scores to a unidimensional model. In other words, the seven TVPS–R subscale scores were used as indicators of a single unidimensional construct (that being motor-free visual perception). If the proposed model fits that data, then empirical evidence is present to support the use of the single summed TVPS–R PQ score because the subscales serve as strong indicators for the same factor or construct. If, for example, the model does not fit the data, then it indicates that the subscales should not be collapsed to create a single total test score because the subscales are measuring different factors. CFA models are assessed using goodness-of-fit indices. Four types of goodness-of-fit indices were used to complete the CFA of the TVPS–R because there is little agreement as to which index provides the best measure of fit. They were chi-square, RMSEA, RMR, and CFI. Results from the CFA are provided in Table 9. Results from the CFA were mixed. Two of the fit indices supported the unidimensional assumption (RMR and CFI) whereas two of the fit indices did not support the TVPS–R one-factor model of motorfree visual perception (chi-square and RMSEA).

Discussion This study examined the measurement properties of the TVPS–R, a frequently used test of motor-free visual-perceptual skills in school-age children (Crowe, 1989; Rodger, 1994). The item analyses, internal consistency, criterion/concurrent validity, and concurrent validity/factor structure of the TVPS–R are discussed. Implications for the TVPS–R’s practical use by clinicians in light of the measurement properties found, are included. Item Analyses The inclusion of items in an instrument is based primarily on the homogeneity of the items within its subscales. Examples of this include item-total scale score correlations and internal consistency. In this study, several of the TVPS–R items had item-total scale score correlation coefficients lower than 0.20 criteria (those being VM 1, VFC 1, VSM 15, and VC 1), thus indicating little or no relationThe American Journal of Occupational Therapy

ship with its corresponding subscale score. If items are unrelated to the subscale they are located in, they are then most likely measuring different skills or qualities. It is, therefore, suggested that the TVPS–R items with correlation coefficients lower than 0.20 be deleted from the next revision of the TVPS–R. In a study completed by Klein et al. (2002), several items from the 1982 version of the TVPS also failed to meet the item-total scale score 0.20 inclusion criteria. It is interesting to note that three of the same subscale items failed to meet the 0.20 correlation criteria in both this study and the Klein et al. study (VM 1, VFC 1, and VC 1). These items are most likely not reflecting the same construct as other items in the subscale and clinicians should be cautious in their use. Internal Consistency The internal consistency reliability of the items on the seven TVPS–R subscales was investigated using the Cronbach (1951) coefficient alpha. In this current study, reliability coefficients varied based on individual age groups by subscale, but not significantly for the total group (Table 4). The TVPS–R PQ reliability coefficient for the age levels ranged between 0.79 and 0.91. The TVPS–R PQ total group reliability coefficient was 0.96. In this study, all total group subscales exhibited acceptable internal consistency reliability. However, none of the subscales showed acceptable reliability (Cronbach’s alpha coefficient of 0.70 or higher) through all of the individual age levels. Therefore, clinicians should consider this in context when using the TVPS–R. In other words, the items of the subscales do not reliably measure children’s visual-perceptual skills across different age levels. Based on individual age groups 6–12 years of age by subscale, reliability coefficients in the Klein et al. (2002) study on the 1982 version of the TVPS varied between VD (0.44–0.88), VM (0.55–0.75), VSR (0.23–0.88), VFC (0.42–0.74), VSM (0.78–0.87), VFG (0.70–0.89), and VC (0.72–0.88). Reliability coefficients by subscale for the total group varied between 0.73 and 0.86. The PQ reliability coefficient ranged between 0.55 and 0.84 (Klein et al., 2002). On the contrary, all total group subscales showed acceptable reliability, although, based on Nunnally and Bernstein’s (1994) suggested 0.70 alpha coefficient value, only three subscales (VSM, VFG, and VC) did so by individual age group whereas the VD, VM, VSR, and VFC subscales exhibited low reliability coefficients. Criterion/Convergent Validity The performance of a group of participants on a test can be checked against a criterion that can either be a direct or an indirect measure of the same or related skill or construct the 189

test is designed to evaluate. The pattern of correlation values were explored between the TVPS–R subscales and a number of established measures, those being the VMI, MVPT–R, and four DTVP–2 motor–motor visual-perceptual subscales. Therefore, if the interpretation of the TVPS–R as a measure of motor-free visual perception is accurate, the TVPS–R subscale scores should correlate well with the other test scores (e.g., VMI, MVPT–R, and DTVP–2) that are known to be related to these skills and abilities. For example, the VMI, MVPT–R, DTVP–2, and TVPS–R all purport to measure VD skills. Using the correlation cut-off points cited in Table 7, it is evident that the TVPS–R subscales present weak criterion/convergent validity compared to other scales that supposedly measure the same construct. The TVPS–R PQ had a higher moderate relationship with the MVPT–R total and DTVP–2 visual-perceptual quotient. The TVPS–R PQ exhibited a low relationship with the VMI, the five MVPT–R subscales, and the four DTVP–2 motor-free subscales. The TVPS–R VD, VM, VSR, VFC, VSM, VFG, and VC subscales all exhibited a low relationship with the VMI, the five MVPT–R subscales, and the four DTVP–2 motor-free subscales. Only the TVPS–R VC subscale exhibited a moderate relationship with the MVPT–R total score, MVPT–R IV scale, and DTVP–2 III scale. The overall scores were only moderately valid compared to other overall measures that claim to be similar. This is surprising because the DTVP–2, MVPT–R, and visual perception subscale of the VMI all purport to measure similar motor-free visual-perceptual constructs common to the TVPS–R. This creates the question as to whether the visual-perceptual constructs measured by these tests are in fact theoretically different. What this demonstrates is that the TVPS–R appears to measure some type of overall visual-perceptual construct, however, when the TVPS–R subscales are compared, they appear to not be correlated. This calls into question the assumption of whether the individual TVPS–R subscales can be summed together to calculate the overall TVPS–R visual-perceptual quotient. In the literature, it has been proposed that the visual-perceptual skills are made up of subskills or subtypes. For example, Frostig, Lefever, and Whittlesey (1966) proposed that visual perception was made up of five components: form constancy, figure ground, position-in-space, spatial relations, and eye–motor coordination. In recent reviews of visual perception, Stephens and Pratt (1989) and Gabbard (1992) confirmed the Frostig’s (1972) visual-perceptual conceptual frameworks. Warren (1993) has developed a hierarchy of visual-perceptual skill development that includes oculomotor control, visual fields, visual acuity, visual attention, scanning, pat190

tern recognition, visual memory, and visual cognition. Schneck (2001) reports that the visual-cognitive components of visual perception include visual attention, visual memory, visual discrimination, and integration of the visual stimulus. The models and conceptual frameworks proposed by Frostig (1972), Warren, and Schneck are not supported by the results of this current study. It appears that the TVPS–R is not measuring a unidimensional construct and is in fact measuring several subconstructs. In the TVPS–R manual, Gardner (1996) reported information concerning concurrent validity and convergent validity that was obtained by correlating the standard scores from the TVPS–R to standard scores from seven other instruments. These included the subscales of the: (a) Test of Visual-Motor Skills–Revised, (b) Test of Auditory Perceptual Skills–Revised, (c) Test of Nonverbal Intelligence, (d) Test of Academic Achievement Skills (reading and arithmetic subtests), (e) Wechsler Preschool and Primary Scale of Intelligence–Revised (vocabulary and picture completion subscales), (f) Weschler Intelligence Scale for Children– Third Edition (vocabulary and picture completion subtests), and (g) Wide Range Achievement Test–Third Edition (reading subscale). The instruments were administered concurrently with the TVPS–R as part of the 1996 standardization and revision process. Correlation coefficients ranged from .12 to .45 between the TVPS–R and the criterion variables. The test developer concluded that these correlations were in the low to moderate range. Gardner (1996) reported that this indicated that the TVPS–R was measuring specific visual-perceptual skills rather than overall intellectual functioning. However, no specific information discussing the criterion variables chosen, or the expected relationship between the TVPS–R and criterion variables was reported in the test manual (Brown, Rodger, & Davis, 2003). Klein et al. (2002) examined the criterion validity of the 1982 version of the TVPS by correlating it with a number of subtests (which included the full-scale standard score, performance standard score, verbal standard score, block design subtest standard score, digit span subtest standard score, vocabulary subtest standard score, and object assembly subtest standard score ) from the Weschler Intelligence Scale for Children–Third Edition (WISC–III) and the Developmental Test of Visual-Motor Integration (VMI). The results indicated that the TVPS perceptual quotient showed a higher relationship with the WISC–III performance standard score than the WISC–III verbal standard score. The TVPS perceptual quotient also exhibited a stronger relationship with the WISC–III block design and object assembly subtest standard scores than the WISC–III digit span and vocabulary subtest standard scores. The digit span subscale exhibited little to no relationship with the March/April 2006, Volume 60, Number 2

TVPS subscales. The intercorrelations between the TVPS subscales and the VMI ranged from .15 to .39 (Klein et al., 2002). Similar to this present study, Klein et al. found that the VMI had only a low correlation relationship with the TVPS and its subscale scores. Construct Validity/Factor Structure Results from the principal component analysis indicate that the majority of the test items across the seven TVPS–R subscales loaded on a dominant first factor. Using the factor loading cut-off of 0.35, it is apparent that only the items of the VD (0.45–0.92), VSR (0.59–0.94), VSM (0.35–0.82), VFG (0.38–0.90), and VC (0.44–0.90) subscales all loaded consistently on the first factor. Only 14 of the 16 items load on the first factor for the VM (0.22–0.80) and VFC (–0.72–0.88). These results present a mixed picture for the subscale factor structure of the TVPS–R with the items for some scales (e.g., VD, VSR, VSM, VFG, and VC) consistently loading on the first factor whereas items for other subscales (e.g., VM and VFC) appear to be multidimensional (meaning that items load on more than one factor, which is undesirable). Based on this analysis, it is unclear whether the same factor is being consistently measured by the different subscales. CFA models were assessed using goodness-of-fit indices. Four types of goodness-of-fit indices were used to complete the CFA of the TVPS–R. Two of the fit indices supported the unidimensional assumption (RMR and CFI) whereas two of the fit indices did not support the TVPS–R one-factor model of motor-free visual perception (chisquare and RMSEA). A unitary motor-free visual-perceptual factor was not found based on the factor structure analysis, and thus the issue of summing the seven TVPS–R subscale scores to calculate the summary PQ score was not supported. In the study completed by Klein et al. (2002), the CFA did not support the use of the 1982 version of the TVPS PQ as representing a unidimensional measure of motor-free visual perception. No exploratory factor analyses or CFAs were reported in the TVPS (1982) or TVPS–R (1996) manuals. All of the items from the visual-spatial relationships subscale consistently loaded on the first factor. Fifteen of the 16 items load on the first factor for the VD, VSM, VFG, and VC subscales, but only 12 of the 16 items loaded on the first factor from the VFC and VM subscales. According to Klein et al., because the items for some subscales consistently loaded on the first factor (e.g., VSR subscale), whereas items for some of the other subscales appeared to be multidimensional (e.g., VFC and VM subscales), these outcomes presented a mixed picture of the TVPS subscale factor structure. A revised version of the TVPS was published in 1996 by The American Journal of Occupational Therapy

Gardner (the TVPS–R), but the unidimensionality question still appears to be problematic. In this study, the results from the confirmatory analysis did not support the unidimensional assumption because the one-factor model provided poor fit to the observed data. In other words, the goodness-of-fit indices were beyond the acceptable level of fit, indicating that the TVPS–R scale data did not fit the hypothesized model. In Klein et al.’s (2002) study, the CFA also did not support the use of the TVPS PQ as representing a unidimensional measure of visual perception. Because of this, Klein et al. cautioned clinicians in their use and interpretation of the TVPS. Study Limitations Generalization of these findings are limited by the fact that the participants involved in the study were a convenience sample. Although the sample represents the age range of the TVPS–R, the sample was not random and therefore may not be representative. Future research using a randomly selected sample would allow investigators to evaluate the generalizability of the results reported in this study. As well, examining the differential item functioning of the TVPS–R subscale items with various diagnostic groups would give clinicians insight into the discriminant validity of the tool. “Further work comparing the performance of children with specific problems to children without apparent problems would facilitate not only the development of better norms, but would also provide evidence of validity” (BuschRossnagel, 1985, p. 1596).

Conclusion This is the first study to report measurement property analysis results from a group of typically developing children that empirically examines the construct of motor-free visual perception as defined by the TVPS–R. A previous study had been completed on the TVPS by Klein et al. (2002) on the 1982 edition of the instrument using performance scores from children with known learning disabilities. The results of this current indicated that several of the TVPS–R items had correlation coefficients lower than 0.20 criteria (those being VM 1, VFC 1, VSM 15, and VC 1) thus indicating little or no relationship with the respective subscale total score. Cronbach’s alpha coefficients by subscale for the total group varied between 0.74 and 0.84. The PQ reliability coefficient for the age levels ranged between 0.79 and 0.91. The PQ total group reliability coefficient was 0.96. All total group subscales exhibit acceptable reliability. However, none of the subscales show acceptable reliability (alpha coefficient of .70 or higher) through all of the age levels. 191

Criterion/convergent validity was explored by examining the correlation between the TVPS–R subscales and the VMI, MVPT–R, and DTVP–2. The TVPS–R PQ showed a higher moderate relationship with the MVPT–R total and DTVP–2 visual-perceptual quotient. The TVPS–R PQ exhibited a low relationship with the VMI, the five MVPT–R subscales, and the four DTVP–2 subscales. The TVPS–R subscales all exhibited a low relationship with the VMI, the five MVPT–R subscales, and the four visual perception DTVP–2 subscales. Only the TVPS–R VC subscale exhibited a moderate relationship with the MVPT–R total score, MVPT–R IV scale, and DTVP–2 III scale. Results from the principal component analysis indicate that the majority of the test items across the seven TVPS–R subscales loaded on a dominant first factor. Confirmatory factor analytic models were assessed using four different goodness-of-fit indices. Two of the fit indices supported the unidimensional assumption (RMR and CFI) whereas two of the fit indices did not support the TVPS–R one-factor model of motor-free visual perception (chi-square and RMSEA). A unitary motor-free visual-perceptual factor was not found, and thus, the issue of the summary PQ score was not supported. The main clinical implication for practitioners is that it is suggested that the TVPS–R PQ not be used as an overall summary performance score of motor-free visual-perceptual abilities, but instead the individual subscale scores be used. Of the seven TVPS–R subscales, five exhibited stronger levels of measurement properties whereas two had less than desirable results (VM and VCF). Based on the data analysis results, it is recommended that clinicians can use five of the TVPS–R subscales with children with confidence: VD, VSR, VSM, VFG, and VC. ▲

Acknowledgments The parents who consented to their children’s participation and the children who volunteered as research subjects are also thanked for their invaluable contribution to the study. Acknowledgements are also extended to the Bloorview Children’s Hospital Foundation, Toronto, Ontario, Canada, for their financial support in the form of a research grant that made the completion of this critical review possible as part of a larger study examining the measurement properties of visual-perceptual instruments used by occupational therapists. Thanks are extended to Ms. Sarah Bernie who provided assistance with the completion of the confirmatory factor analysis under the supervision of the second author. Results of this paper were presented at the Children’s Hospital of Eastern Ontario Research Rounds, Ottawa, Ontario, Canada in September 2002 and at the 192

2nd Annual Paediatric Occupational Therapy Conference, Brisbane, Queensland, Australia, in October 2003.

References Anastasi, A., & Urbina, S. (1997). Psychological testing. Upper Saddle River, NJ: Prentice Hall International. Asher, I. E. (1996). Occupational therapy assessment tools: An annotated index. Rockville, MD: American Occupational Therapy Association. Beery, K. E. (1997). The Beery-Buktenica Developmental Test of Visual-Motor Integration with supplemental developmental tests of visual perception and motor coordination: Administration, scoring and teaching manual. Parsippany, NJ: Modern Curriculum Press. Bentler, P. M. (1990). Comparative fit indexes in structural models. Psychological Bulletin, 107, 238–246. Bentler, P. M., & Bonett, D. G. (1980). Significance tests and goodness of fit in the analysis of covariance structures. Psychological Bulletin, 88, 588–606. Bishop, K., & Curtin, M. (2001). The TVPS, MVPT and VMI: What influences a therapist’s choice? National Association of Paediatric Occupational Therapy Journal, 5(1), 8–11. Bollen, K. A., & Long, J. S. (1993). Testing structural equation models. Newbury Park, CA: Sage. Bouska, M. J., Kauffman, N. A., & Marcus, S. E. (1990). Disorders of the visual-perceptual system. In D. A. Umphred (Ed.), Neurological rehabilitation (pp. 705–740). St. Louis: Mosby. Brown, G. T., Rodger, S., & Davis, A. (2003). Test of VisualPerceptual Skills–Revised: A review and critique. Scandinavian Journal of Occupational Therapy, 10, 3–15. Browne, M. W., & Cudek, R. (1993). Alternative ways of assessing model fit. In K. A. Bollen & J. S. Long (Eds.), Testing structural equation models. Newbury Park, CA: Sage. Burtner, P., McMain, M., & Crowe, T. (2002). Survey of occupational therapy practitioners in southwestern schools: Assessments used and preparation of students for schoolbased practice. Physical & Occupational Therapy in Pediatrics, 22, 25–38. Busch-Rossnagel, N. A. (1985). Review of the Test of VisualPerceptual Skills (Non-Motor). In J. V. Mitchell (Ed.), The ninth mental measurements yearbook (pp. 1595–1596). Lincoln, NE: Buros Institute of Mental Measurements. Case-Smith, J. (2001). Use of standarised tests in paediatric practice. In J. Case-Smith, A. S. Allen, & P. T. Pratt (Eds.), Occupational therapy for children (pp. 217–245). Toronto, Ontario, Canada: Mosby. Chia, S. H. (1997). Occupational therapists’ assessment practices with children who have disabilities. British Journal of Therapy & Rehabilitation, 4, 123–128. Chu, S., & Hong, S. C. (1997). A review of assessments used in paediatric occupational therapy. British Journal of Therapy and Rehabilitation, 4, 228–233. Cohen, J. (1988). Statistical power analysis for the behavioral sciences. Hillsdale, NJ: Erlbaum. Colarusso, R. P., & Hammill, D. D. (1996). Motor-Free Visual Perception Test–Revised. Novato, CA: Academic Therapy Publications. March/April 2006, Volume 60, Number 2

Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16, 297–334. Crowe, T. K. (1989). Pediatric assessments: A survey of their use by occupational therapists in northwestern school systems. Occupational Therapy Journal of Research, 9, 273–286. Denison, J. W. (1985). Review of the Test of Visual-Perceptual Skills (Non-Motor) In J. V. Mitchell (Ed.), The ninth mental measurements yearbook (pp. 1596–1598). Lincoln, NE: Buros Institute of Mental Measurements. Erhardt, R. P., & Duckman, R. H. (1997). Visual-perceptualmotor dysfunction. In M. Gentile (Ed.), Functional visual behavior: A therapist’s guide to evaluation and treatment options (pp. 133–196). Rockville, MD: American Occupational Therapy Association. Feder, K. P., Majnemer, A., & Synnes, A. (2000). Handwriting: Current trends in occupational therapy practice. Canadian Journal of Occupational Therapy, 67, 197–204. Frostig, M. (1972). Visual perception, integrative functions and academic learning. Journal of Learning Disabilities, 5, 5–19. Frostig, M., Lefever, D. W., & Whittlesey, J. R. B. (1966). Administration and scoring manual for the Marianne Frostig Developmental Test of Visual Perception. Palo Alto, CA: Consulting Psychologists Press. Gabbard, C. (1992). Lifelong motor development. Dubuque, IA: Wm. C. Brown. Gardner, M. F. (1982). Test of Visual-Perceptual Skills (Non-Motor). San Francisco: Psychological and Educational Publications. Gardner, M. F. (1996). Test of Visual-Perceptual Skills (NonMotor)–Revised. San Francisco: Psychological and Educational Publications. Gentile, M. (1997). Functional visual behavior: A therapist’s guide to evaluation and treatment options. Rockville, MD: American Occupational Therapy Association. Hammill, D. D., Pearson, N. A., & Voress, J. K. (1993). Developmental Test of Visual Perception (2nd ed). Austin, TX: Pro Ed. Hung, S. S., Fisher, A. G., & Cermak, S. A. (1987). The performance of learning-disabled and normal young men on the Test of Visual-Perceptual Skills. American Journal of Occupational Therapy, 41, 790–797. Kim, J., & Mueller, C. W. (1978). Factor analysis: Statistical methods and practical issues. Newbury Park, CA: Sage. Klein, S., Sollereder, P., & Gierl, M. (2002). Examining the factor structure and psychometirc properties of the Test of Visual-Perceptual Skills. Occupational Therapy Journal of Research: Occupation, Participation and Health, 22, 16–24. Kline, P. (1986). A handbook of test construction: Introduction to psychometric design. New York: Methren & Co. Law, M., Baum, C., & Dunn, W. (2001). Measuring occupational performance: Supporting best practice in occupational therapy. Thorofare, NJ: Slack. Long, J. S. (1983). Confirmatory factor analysis. Newbury Park, CA: Sage. McFall, S. A., Deitz, J. C., & Crowe, T. K. (1993). Test–retest reliability of the Test of Visual-Perceptual Skills with children with learning disabilities. American Journal of Occupational Therapy, 47, 819–824.

The American Journal of Occupational Therapy

Miller, L. T., Missiuna, C. A., MacNab, J. J., Mallory-Miller, T., & Polatajko, H. J. (2001). Clinical description of children with developmental coordination disorder. Canadian Journal of Occupational Therapy, 68, 5–15. Norman, G. R., & Streiner, D. L. (1994). Biostatistics: The bare essentials. Toronto, Ontario, Canada: Mosby. Nunnelly, J., & Bernstein, I. (1994). Psychometric theory. New York: McGraw-Hill. Plapinger, D. S., & Sikora, D. M. (1995). The use of standardized test batteries in assessing the skill development of children with mild-to-moderate sensorineural hearing loss. Language, Speech, and Hearing Services in Schools, 26, 39–44. Reid, D. (1987). Occupational therapists’ assessment practices with handicapped children in Ontario. Canadian Journal of Occupational Therapy, 54, 181–188. Reid, D., & Drake, S. (1990). A comparative study of visual-perceptual skills in normal children and children with diplegic cerebral palsy. Canadian Journal of Occupational Therapy, 57, 141–146. Reid, D., & Jutai, J. (1997). A pilot study of perceived clinical usefulness of a new computer-based tool for assessment of visual perception in occupational therapy practice. Occupational Therapy International, 4, 81–89. Rodger, S. (1994). A survey of assessments used by paediatric occupational therapists. Australian Occupational Therapy Journal, 41, 137–142. Schneck, C. M. (1996). Visual perception. In J. Case-Smith, A. S. Allen, & P. T. Pratt (Eds.), Occupational therapy for children (pp. 357–385). Toronto, Ontario, Canada: Mosby. Schneck, C. M. (2001). Visual perception. In J. Case-Smith (Ed.), Occupational therapy for children (pp. 382–412). Toronto, Ontario, Canada: Mosby. Schneck, C. M., & Lemer, P. S. (1993). Reading and visual perception. In C. B. Royeen (Ed.), AOTA self-study series: Classroom applications for school-based practice (pp. 1–48). Rockville, MD: American Occupational Therapy Association. Stephens, L. C., & Pratt, P. N. (1989). School work tasks and vocational readiness. In P. N. Pratt & A. S. Allen (Eds.), Occupational therapy for children (pp. 311–324). St. Louis, MO: Mosby. Streiner, D. L., & Norman, G. R. (1995). Health measurement scales: A practical guide to their development and use. Oxford, England: Oxford University Press. Wallen, M., & Walker, R. (1995). Occupational therapy practice with children with perceptual motor dysfunction: Findings of a literature review and survey. Australian Occupational Therapy Journal, 42, 15–25. Warren, M. (1993). A hierarchical model for evaluation and treatment of visual-perceptual dysfunction in adult acquired brain injury. Part 1. American Journal of Occupational Therapy, 47, 42–54. Weil, M. J., & Amundson, S. J. C. (1994). Relationship between visuomotor and handwriting skills of children in kindergarten. American Journal of Occupational Therapy, 48, 982–988.

193