Research Article
Classification Accuracy of Nonword Repetition When Used With Preschool-Age Spanish-Speaking Children Mark Guibersona and Barbara L. RodrõÂguezb
Purpose: The purpose of the present study was to (a) describe and compare the nonword repetition (NWR) performance of preschool-age Spanish-speaking children (3- to 5-year-olds) with and without language impairment (LI) across 2 scoring approaches and (b) to contrast the classification accuracy of a Spanish NWR task when item-level and percentage of phonemes correct (PPC) scoring methods are applied. Method: Forty-four Spanish-speaking children participated. Twenty-one children had LI and 23 had typically developing (TD) language. Children were administered a Spanish NWR task and a standardized Spanish language measure. Results: A developmental pattern in NWR performance was observed, and the children with LI had NWR scores that were
I
n 2008, Latinos accounted for 22% of the students enrolled in public schools, and Spanish-speaking children represented the largest portion of young English language learners (Fortuny, Hernandez, & Chaudry, 2010). Nationally, 28% of preschool-age children were from households where a language other than English was spoken, and the majority of these children were from Spanishspeaking backgrounds (U.S. Census Bureau, 2008). In the coming years, this growth trend is expected to continue (Center for Public Education, 2012). The increasing presence of young Spanish-speaking children in U.S. preschool classrooms requires language assessment measures to be developed for this growing segment of the population. Accurate and reliable Spanish assessment measures are needed to differentiate children with language impairment (LI) from children who have typically developing (TD) language. A Spanish nonword repetition (NWR) task may a
University of Wyoming, Laramie The University of New Mexico, Albuquerque
b
Correspondence to Mark Guiberson:
[email protected] Editor: Marilyn Nippold Associate Editor: Gary Troia Received January 19, 2012 Revision received April 3, 2012 Accepted October 22, 2012 DOI: 10.1044/0161-1461(2012/12-0009)
significantly lower than those of the TD children. Whereas item-level scoring of NWR items indicated acceptable levels of sensitivity and specificity and suggested positive and negative likelihood ratios, PPC scoring of NWR items resulted in less than desirable levels of sensitivity and adequate specificity. Conclusion: Item-level scoring of 3- to 5-syllable Spanish NWR items may be useful as part of an assessment battery for preschool-age Spanish-speaking children. Key Words: nonword repetition, Spanish-speaking, classification accuracy
provide useful information that could assist in identifying LI in Spanish-speaking children. NWR is a brief processdependent task that is designed to minimize biases associated with traditional language assessment measures. Nonword repetition has been suggested as a possible phenotypic marker for some forms of LI (Bishop, North, & Donlan, 1996). Although numerous studies have examined the NWR skills of English-speaking children, the NWR skills of Spanish-speaking children, particularly those of preschool age, need to be examined.
NWR NWR is a task in which children are asked to repeat novel phonological forms or nonsense words such as /naõb/ (Archibald, 2008). NWR mimics an important language learning mechanism: immediate repetition of unfamiliar words (Archibald, 2008). NWR tasks have been argued to tap into underlying cognitive skills, including phonological working memory, phonological encoding, phonological awareness or sensitivity, and a general phonological processing ability (for a review, see Graf Estes, Evans, & ElseQuest, 2007). NWR tasks are also thought to be languagebased processing measures that theoretically deemphasize prior language experiences (Dollaghan & Campbell, 1998; Kohnert, Windsor, & Yim, 2006). Nonword characteristics. Nonword stimuli have specific characteristics (Dollaghan & Campbell, 1998; Graf Estes
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et al., 2007; Kohnert et al., 2006). For example, nonwords adhere to the phonotactic constraints of the language they are intended for, using conventional speech sounds combined in permissible ways; they have no semantic value; and they do not correspond to words that exist in the given language. Nonwords can vary in syllable length, with items ranging from one to four syllables for English NWR tasks and from one to five syllables for Spanish NWR tasks. The developmental difficulty of phonemes included in nonwords can vary, with some NWR stimuli designed to reduce articulatory difficulty and to include the most frequently occurring phonemes in a specific language. NWR administration and elicitation approaches. Most researchers present audio-recorded stimuli when administering NWR tasks. This administration approach is especially appropriate for participants who are school age and older (Archibald, 2008; Dollaghan & Campbell, 1998). Several recent studies that included toddler and preschool-age children have modified the NWR administration procedures. Some of the more common modifications have included live presentation of nonwords and/or interactive strategies that incorporate play (e.g., ball rolling or use of a puppet or figurine). These interactive strategies help make NWR tasks developmentally appropriate, thereby enhancing young children's attention better than listening to and repeating recorded NWR items (Chiat & Roy, 2007; Stokes & Klee, 2009). A disadvantage to live presentation is that a certain amount of variability in rate, pitch, and volume of the production of the items may occur. Despite this disadvantage, live presentation is more natural, clinically relevant, and comparable to the delivery mode of other clinical assessment activities (Archibald, 2008; Chiat & Roy, 2007). NWR scoring approaches. Two scoring approaches are frequently used in NWR studies: percentage of phonemes correct (PPC) and item-level scoring (Graf Estes et al., 2007). In PPC scoring, audio recordings of the children's repetitions are collected and reviewed, and a child's repetition of each phoneme in every nonword is scored as correct or incorrect. The total number of correct phonemes is divided by the total number of phonemes to obtain the PPC for each syllable length presented. In contrast, in item-level scoring, the child's repetition of entire nonwords is scored as correct or incorrect. The total number of items repeated correctly is then tallied for each syllable length presented. Item-level scoring can be completed online immediately after each item is presented. This scoring method is clinically practical because it does not require the time-consuming PPC scoring steps of reviewing audio recordings and completing additional calculations (Archibald, 2008). Aside from being more clinically practical, there are other reasons that item-level scoring may be preferred over PPC scoring. In several NWR studies in which PPC and item-level scores were completed, very high correlations (r = .90±.95, p = ,.001) were observed for the two scoring methods, thus providing support for the use of the simpler of the two scoring methodsÐitem-level scoring (Archibald, 2008; Archibald & Gathercole, 2006). Furthermore, large
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effect sizes have been observed in studies that compared item-level scores of LI and TD groups (Graf Estes et al., 2007). Item-level scoring may be a more sensitive scoring approach because it does not give children with LI any credit for partially correct repetition of nonwords (e.g., when some but not all phonemes are repeated correctly), whereas with a PPC scoring approach, children are given credit for each correct phoneme in a nonword. NWR in English-speaking children with LI. Studies of NWR with English-speaking children have shown that children with LI have substantial difficulty with NWR (for a review, see Graf Estes et al., 2007). A meta-analysis of 23 studies revealed that children with LI performed on average more than 1 SD below TD children on NWR tasks, with a weighted mean effect size of 1.27 (95% confidence interval [CI] = [1.15±1.39]; Graf Estes et al., 2007). These very large effect sizes also had significant variability across studies, indicating that differences in NWR performance varied by study. Further analyses revealed that the length of the nonwords was associated with the magnitude of the effect size, whereas the age of the participants was not. NWR tests that include a high proportion of longer nonwords may separate children with LI from TD children because longer words may tax the phonological working memory of children with LI to a greater extent than they do for TD children (Graf Estes et al., 2007). Results from the meta-analysis indicated that NWR is useful in detecting group differences between school-age children with and without LI, but that more research describing younger children's performance on NWR tasks is needed. Differences in NWR performance between TD and LI groups are important, but alone, they do not inform how well the task distinguishes children with LI from TD children. Classification accuracy measures (e.g., sensitivity, specificity, and positive and negative likelihood ratios [+LR, ±LR]) provide specific information about individual-level performance and are strong psychometric indicators of how useful a task may be in identifying individuals who have an impairment (Dollaghan, 2007). Studies that have described the sensitivity and specificity of NWR tasks when used with school-age children have yielded mixed results. Both acceptable classification accuracy values (Archibald & Alloway, 2008; Dollaghan & Campbell, 1998; Gray, 2003) and lower levels of sensitivity but acceptable specificity have been reported (Conti-Ramsden, 2001; Conti-Ramsden & Hesketh, 2003; Ellis Weismer et al., 2000).
NWR in Toddler and Preschool-Age EnglishSpeaking Children Recent studies have described NWR in toddler- and preschool-age English-speaking children. Hoff, Core, and Bridges (2008) reported on two small sample studies that described the association between vocabulary and NWR skills in young children. Both studies included children between 20 and 24 months of age and used live administration of nonwords in combination with a PPC scoring approach. In the first study, children's (N = 15) performance
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on a 9-item NWR task was significantly correlated with vocabulary as measured by the Communicative Development Inventory (CDI; Fenson et al., 2007, r = .72, p , .001). Similarly, in the second study, children's (N = 21) performance on a 12-item NWR task was significantly correlated with vocabulary as measured by the CDI short form (r = .53, p , .01). These findings offer support for the relationship between NWR performance and early linguistic development in toddler-age children. In another study, Chiat and Roy (2007) examined and compared the NWR performance of two groups of young children ages 2;6 (years;month) to 4;0: a typical group (n = 315) and a clinical group (n = 168). The NWR task from the Preschool Repetition Test (Roy & Chiat, 2004) was used, and live, active engagement strategies were applied. The NWR performance of both the typical group and the clinical group improved with age, but the clinical group performed noticeably more poorly than the typical group did across the 1- to 5-syllable NWR tasks. The clinical group's mean total NWR score at each 6-month age interval was 1.6±2.0 SD below those of the typical group. When group comparisons (typical vs. clinical) by 6-month age intervals were completed, significant group differences (p , .001) were observed in children ages 2;6 to ,3;0, 3;0 to ,3;6, and 3;6 to ,4;0. Stokes and Klee (2009) described group differences and the classification accuracy of 1- to 3-syllable and 1- to 4-syllable versions of the Test of Early Nonword Repetition with 2-year-olds with and without delayed language. An interactive administration approach that included live administration of NWR items and a ball-rolling activity were applied, and PPC scoring was used. For the 1- to 3-syllable items, significant group differences were detected (N = 177), as well as acceptable sensitivity (75%) and specificity (90%) and very positive (7.8) and moderately negative (.28) LRs. For the 1- to 4-syllable items, significant group differences were also detected (N = 96), as well as acceptable sensitivity (88%) and specificity (94%) and very positive (14.88) and very negative (.13) LRs. The findings from this study indicated that improved classification accuracy can be obtained with English NWR tasks when longer items (4-syllable NWR items) are used. Viewed together, the results from these studies of young English-speaking children provide support for the use of interactive NWR administration procedures with young children.
NWR in Spanish-Speaking and Spanish±English Bilingual Children Recent studies have described the NWR performance of Spanish-speaking and bilingual children with and without LI. All of the studies described in the following paragraphs used Spanish NWR tasks that followed the phonotactic rules of Spanish. For example, the NWR items included phonemes and consonant vowel patterns that are common in Spanish as well as permissible phoneme combinations. Items also followed the prosodic and phonological patterns of Spanish (e.g., Spanish words tend to be longer than English words). Two of the Spanish NWR tasks developed in previous
research include NWR items that are five syllables in length (Ebert, Kalanek, Cordero, & Kohnert, 2008; Girbau & Schwartz, 2007). It is important that these NWR tasks were developed with Spanish phonotactic rules in mind because a child's language environment provides examples of the word shapes and phonological patterns that occur in that language (Summers, Bohman, Gillam, PenÄa, & Bedore 2010). Girbau and Schwartz (2007) completed a study that compared the NWR performance of school-age Spanishspeaking children with and without LI. This study was conducted in Spain with 22 children of middle socioeconomic backgrounds from bilingual families. The NWR stimuli included 20 items ranging from one to five syllables in length. The NWR items included consonant clusters. Children with LI performed more poorly than their TD peers, with significant group differences detected for items that were three to five syllables in length. Classification accuracy was examined using item-level scores. Results indicated that the NWR task had strong classification accuracy, providing preliminary evidence that Spanish NWR tasks may be useful for diagnostic purposes. However, Girbau and Schwartz cautioned that their classification accuracy values may be somewhat inflated because they were based on preselected groups of children with and without LI and very specific selection criteria. Two recent studies completed in the United States described the performance of TD Spanish±English bilingual samples on Spanish NWR tasks. In the first study, a Spanish NWR task was administered to 14 preschool-age children who spoke primarily Spanish but also had some exposure to English (Ebert et al., 2008). The goals of this study were to describe the association between NWR and language measures and to describe developmental patterns and agerelated differences in NWR performance. The sample was split into a younger group (ages ranging from 3;6 to 4;0) and an older group (ages ranging from 4;3 to 5;6). The English and Spanish editions of the Preschool Language Scale, Fourth Edition (PLS±4 and SPLS±4; Zimmerman, Steiner, & Pond, 2002a, 2002b) were administered in order to compare NWR with language scores. A PPC scoring method was applied to examine NWR performance. NWR PPC was not significantly associated with the Spanish (r = .29, p = .39) or English PLS±4 scores (r = .41, p = .21), but clear developmental trends were evident in the children's NWR performance. A significant Age 6 Syllable Length interaction was observed, with younger children demonstrating more difficulty than older children with longer NWR items. In the second study, the NWR skills of children between 4 and 6 years of age with varying degrees of Spanish and English exposure and usage were described (Summers et al., 2010). Parent surveys were used to gather language usage and exposure data, and the Bilingual English Spanish Assessment (PenÄa, GutieÂrrez-Clellen, Iglesias, Goldstein, & Bedore, 2009) was used to measure Spanish and English morphosyntax. Two NWR tasks were presented. The first NWR task included 16 English-like nonwords ranging from one to four syllables in length (Dollaghan & Campbell, 1998). The second NWR task included 20 Spanish-like
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nonwords ranging from two to four syllables in length (Calderon, 2003). PPC scoring methods were applied. Several mixed models of analysis of variance were completed to detect relationships between NWR and the predictor variables. Significant main effects were observed for English morphosyntax and English nonword length (R2 = 0.28, p = ,.001) as well as Spanish morphosyntax, Spanish language usage/output, and Spanish nonword length (R2 = .28, p = ,.001). Significant interactions were detected between nonword length and age of first exposure to English for English nonwords (R2 = .05, p = ,.01) and Spanish nonwords (R2 = .06, p = ,.01). These results indicate that morphosyntax, language usage, and language exposure factors are associated with bilingual children's NWR performance. Several studies have also described the NWR performance of school-age Spanish and/or Spanish±English bilingual children with LI in the United States. Kohnert et al. (2006) described the NWR performance of school-age children (N = 100) between 7 and 13 years of age. The sample included English-speaking children with LI, TD Englishspeaking children, and TD Spanish±English bilingual children. Kohnert et al. used Dollaghan and Campbell's English NWR task (1998) and employed a PPC scoring method. The English-speaking children with LI scored most poorly on the task. The TD English-speaking children had the strongest scores, and the TD bilingual children's scores fell in between the other two groups' scores. The LRs obtained in this study revealed substantial overlap between the LI English-speaking and TD bilingual groups, indicating poor classification accuracy. However, the classification accuracy values obtained in this study may have been inadequate because a Spanish NWR measure was not employed, and some bilingual children may have demonstrated improved performance on a Spanish NWR task. In another study, the NWR performance of school-age children (N = 187) with and without LI from English and Spanish language backgrounds was described (Windsor, Kohnert, Lobitz, & Pham, 2010). Parent report of family language usage and language used in an educational setting established a child's first language and bilingual status. An English NWR task (Dollaghan & Campbell, 1998) and a Spanish NWR task (Ebert et al., 2008) were administered, and a PPC scoring approach was applied. Overall, the children performed better in their first language, and the children with LI performed more poorly than their TD peers. Also, a significant correlation between NWR performance across languages was observed for the TD bilingual children (r = .71, p = ,.01), but not for the children with LI (r = .19). Significant group differences in NWR performance were observed, with language background and LI status influencing performance. Windsor et al. (2010) also found group differences in children's performance on items five syllables in length and suggested that performance on items of increasing length may be especially informative in separating the group with LI from the TD bilingual group. Adequate classification accuracy was achieved for the TD bilingual children when
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NWR performance on both the English and Spanish tasks were taken into account, suggesting that for school-age bilingual children, it is important to consider performance in both languages. Finally, GutieÂrrez-Clellen and Simon-Cereijido (2010) described the NWR performance of 144 bilingual children between 3 and 7 years of age with and without LI. Parent and teacher questionnaires documented that children's exposure to Spanish and English varied, resulting in 63 Spanish-dominant and 71 English-dominant children. Dollaghan and Campbell's (1998) English NWR items were administered in addition to a set of 20 Spanish nonwords two to four syllables in length that demonstrated favorable qualities in an earlier study (Calderon, 2003). Children's performance was scored using a PPC scoring method. The highest +LR (9.71) and high specificity (96%) resulted from combining the results from both the Spanish and English NWR tasks and using a 70% accuracy cutoff score on each task; however, the sensitivity (41%) and 2LR (.62) obtained were undesirable. GutieÂrrez-Clellen and Simon-Cereijido concluded that Spanish NWR measures with longer nonwords may yield better classification accuracy qualities than Spanish NWR measures with shorter words. Classification accuracy of Spanish NWR tasks. An important step in evaluating Spanish NWR tasks is describing how accurately they classify individuals as disordered or not disordered. In the following section, we present classification accuracy descriptions and decision rules as described by Dollaghan (for a review, see Dollaghan, 2007). Sensitivity, specificity, +LR, 2LR, and respective CIs are the most frequently reported classification accuracy statistics (Dollaghan, 2004). Sensitivity is the proportion of individuals positive for the disorder who are correctly identified as such by the tool; specificity is the proportion of individuals negative for the disorder who are correctly identified as such by the tool. Sensitivity and specificity are susceptible to the variation of an individual sample and are not recommended as primary measures of classification accuracy. However, +LR and 2LR are robust to variations in base rate (the percentage of the people with the disorder in the sample) and therefore are preferred classification accuracy measures, especially when associated CIs are reported. A +LR indicates the degree of confidence that a person who scores in the positive range on the tool truly has the target disorder. A +LR §10 can be interpreted to very likely indicate disorder, a +LR = 3 is suggestive but insufficient to diagnose the disorder, and a +LR = 1 indicates that results from the tool are uninformative for diagnosing the disorder. A 2LR indicates the degree of confidence that a person who scores in the negative range does not have the disorder. A 2LR ¦.10 can be interpreted to very likely rule out the disorder, a 2LR ¦.30 is suggestive but insufficient to rule out the disorder, and a 2LR value = 1 indicates that results from the tool are uninformative for ruling out the disorder. LRs are preferred classification accuracy measures, but because CIs are point estimates, it is important to also consider associated CIs because CIs indicate the range of possible LR values and describe the tool's precision.
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Table 1. Sensitivity, specificity, positive likelihood ratio (+LR), and negative likelihood ratio (2LR) based on Spanish nonword repetition (NWR) data from earlier studies. Sensitivity
Kohnert, Windsor, & Yim (2006) Girbau & Schwartz (2007) Windsor, Kohnert, Lobitz, & Pham (2010) Gutierrez-Clellen & Simon-Cereijido (2010)
Specificity
LR (95% CI)
#
%
#
%
+
2
14/28 11/11 11/19 30/49
50 100 58 61
65/71 10/11 53/65 78/95
92 91 82 82
5.92 (2.53±13.85) 11.00 (1.70±71.28) 3.14 (1.66±5.94) 3.42 (2.11±5.56)
.55 (.37±.80) 0 (N/A)a .52 (.30±.89) .47(.33±.68)
Note. Values were rounded to the nearest integer. CI = confidence interval. a
CIs could not be calculated with certainty because of the lack of variability observed.
For the purpose of comparing studies that have reported on the classification accuracy of Spanish NWR tasks, we closely reviewed each study and collected classification accuracy values or raw data reported for studies including children with and without LI. We used this information to compute sensitivity, specificity, +LR, 2LR, and corresponding CIs. The Spanish NWR classification accuracy measures for the four studies are presented in Table 1. The +LR obtained on Spanish NWR tasks ranged from 3.14 to 11.00. Three of the four studies reviewed had suggestive +LR and relatively narrow CIs that were above the uninformative range. The study with the strongest +LR (Girbau & Schwartz, 2007) was completed with a rather small sample (N = 22) and had extremely broad +LR CIs; these characteristics suggest that the tool may lack precision in classifying children (Dollaghan, 2004; Dollaghan & Horner, 2011). The 2LR obtained on three of the Spanish NWR tasks ranged from .47 to .55, with narrow corresponding CIs. These 2LR values indicated that the Spanish NWR tasks yielded results that are suggestive but insufficient to rule out disorder. For the fourth study (Girbau & Schwartz, 2007), 2LR was 0 and corresponding CIs could not be calculated because of the lack of variability observed. As stated earlier, this lack of variability is a cause for concern and should be interpreted with caution, at least until these results have been replicated in multiple carefully conducted large-scale studies with this diagnostic measure (Dollaghan, 2007). Based on the classification accuracy measures of the other three studies, Spanish NWR tasks may provide useful information when attempting to identify LI in school-age Spanish-speaking children.
Current Study The NWR meta-analysis and studies of preschool-age English-speaking children, combined with the emergent body of NWR research describing Spanish-speaking and Spanish± English bilingual children, indicate the need for additional studies describing the Spanish NWR performance of preschool-age children with and without LI. Such studies will help determine the usefulness of Spanish NWR tasks as a diagnostic marker for LI in preschool-age Spanish-speaking children. Available measures intended to diagnose LI in Spanish-speaking children are only somewhat suggestive
of diagnostic status because either they lack acceptable classification accuracy or they have precision values that are uninformative (Dollaghan & Horner, 2011). Furthermore, there is a need to contrast results obtained through item-level and PPC scoring methods. Given the effort required to complete PPC scoring and the relative ease of item-level scoring, these findings may have practical applications if NWR tasks are to be included as a component of comprehensive language assessments. The purpose of the present study was to (a) describe and compare the NWR performance of preschool-age Spanish-speaking 3-, 4-, and 5-year-olds with and without LI across two scoring approaches and (b) to contrast the classification accuracy of a Spanish NWR task when itemlevel and PPC scoring methods are applied.
Method Participants Forty-four preschool-age children (3;0±5;10) participated in this study. Families were recruited from two regional Head Start and Early Head Start programs in the western United States. Children met the following inclusionary criteria: normal hearing, no known neurological impairment, and lack of severe phonological impairment. Only predominantly Spanish-speaking children (who spoke Spanish §80% of the time according to parent report) were included.1 In order to maximize statistical power for group comparisons, we determined at the onset of the study that the sample would be approximately split in terms of LI status. Three sources were obtained to establish LI status: (a) identification of LI by a bilingual speech-language pathologist (SLP), (b) report of parent concerns about child's language development, and (c) expressive language scores on the SPLS±4 ¦77 (1.5 SDs below the mean). Children were placed in the TD group if (a) they had not been previously diagnosed as having LI, (b) their parents did not report concerns about their language development, and (c) they had expressive language SPLS±4 scores §85. 1 The term Spanish-speaking will be used to refer to this sample for the remainder of the manuscript.
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LI from TD children. Second, this particular task was developed to minimize interference from articulatory limitations on task performance, which was an especially important consideration given that the current study included preschool-age children. The NWR items on this task included only consonants that are acquired early by Spanish-speaking children and not consonant clusters. Girbau and Schwartz's (2007) Spanish NWR task was considered because it includes 5-syllable items, but it was not selected because the items included consonant clusters as well as later developing phonemes, which did not minimize interference from articulatory limitations. Finally, we selected the Ebert et al. task so that the results from our study could be compared easily to other studies involving samples of preschool-age Spanish-speaking children residing in the United States. The Ebert et al. (2008) NWR task consists of 20 nonword stimuli that follow Spanish phonotactic constraints and phoneme frequency patterns. The NWR stimuli were developed based on a consonant-vowel (CV) syllable structure that is common in Spanish. The nonwords also maintained the Spanish pattern of stress on the penultimate syllable. The items gradually increase in syllable length (from one to five syllables), with four items for each syllable length presented. A complete list of the NWR items and more detailed information about item development and criteria are provided in Ebert et al. (2008). Information about internal consistency among the NWR items at each syllable length was not reported in the norming study or in subsequent studies that have used this task. As a preliminary step, the internal consistency for the total set of NWR items was calculated for the current sample (N = 44). Acceptable internal consistency was observed (a = .81), and removal of individual items did not influence the acceptability of the internal consistency coefficients (Gliner, Morgan, & Leech, 2009). SPLS±4. The SPLS±4 was developed from a Spanishlanguage model and was standardized on 1,188 Spanishspeaking children living in the United States from monolingual Spanish or mostly Spanish bilingual households. An SPLS±4 normative study (n = 575) indicated strong test±retest reliability (.77±.86) and split-half internal consistency (.80±.90). In a concurrent validity study (n = 140),
Based on these criteria, the LI group included 21 children (16 boys and 5 girls) and the TD group included 23 children (13 boys and 10 girls); there were no significant group differences in terms of gender: x2(1, N = 44) = 1.89, p = .17. There were also no significant group differences in the children's age, mothers' percentage of Spanish usage with the child, or children's percentage of Spanish usage with the parents (see Table 2). As mentioned earlier, the children who participated in this study were enrolled in either Head Start or Early Head Start programs. There was no significant group difference between the LI and TD groups in terms of the type of program enrollment: x2(1, N = 44) = .31, p = .58. Two language-of-instruction models, primarily Spanish instruction or Spanish + English instruction, were employed by these programs either in the classroom (Head Start) or during home visits and center visits (Early Head Start). Detailed information about the Spanish + English instructional model was not available, nor was peer-to-peer language usage data. However, teacher interviews were completed to describe the language-of-instruction models that were used in the Spanish + English classrooms; these teachers reported that Spanish was used between 50% and 75% of the time. Twenty-six (59%) of the children received primarily Spanish instruction, and 18 (41%) received Spanish + English instruction. Analyses were completed to establish that NWR performance was not confounded by the language of instruction. There were no significant language-ofinstruction group differences on the SPLS±4 expressive language standard scores, t(42) = 21.51, p = .14; NWR total PPC scores, t(42) = 2.71, p =.48; or NWR total item-level scores, t(42) = 2.96, p = .34. An additional analysis was completed to determine if the LI or TD groups differed in terms of their language of instruction, and no significant group differences were detected, x2(1, N = 44) = .95, p = .33.
Measures NWR. We used the Spanish NWR task that was developed by Ebert et al. (2008) as the NWR measure. We selected this particular NWR task for several reasons. First, this task contains items up to five syllables in length, which several studies of school-age Spanish-speaking children have indicated may be important in separating out children with
Table 2. Means, standard deviations, and independent-samples t test for family and child characteristics for the typically developing (TD) group and the group with language impairment (LI). TD group (N = 23)
Age (years; months) Mother's % Spanish with child Child's % Spanish with parents SPLS±4 expressive language
LI group (N = 21)
M
SD
M
SD
t test
p
4;1 95% 95% 99.04
.82 8% 5% 7.00
3;11 97% 97% 71.33
0.81 5% 8% 8.12
2.73 1.73 1.29 227.10
.47 .09 .20 ,.001*
Note. SPLS±4 = Preschool Language Scales, Fourth EditionÐSpanish Edition (Zimmerman, Steiner, & Pond, 2002b). *p , .001.
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the comprehension section of the SPLS±4 demonstrated good sensitivity (.83±.91) but rather low specificity (.57±.55), and the expressive section demonstrated acceptable classification accuracy (sensitivity =.92±.91, specificity = .77±.61). The expressive subtest of the SPLS±4 was used in the current study as one of three data sources used for assigning children to the LI or TD group.
Procedure Before data collection, we determined that roughly half of the children to be included in the study would have LI and half would be TD. General recruitment efforts included sending home flyers through Head Start programs and participating in health and literacy fairs and family night events hosted by these programs. In addition, the investigators collaborated with disability coordinators or SLPs from the cooperating programs to recruit families with children who had been identified as having LI. Interested families who met the inclusionary criteria were presented with an informed consent form in Spanish that had been approved by the University of Wyoming's Institutional Review Board. Families who consented to participate in the study were given a demographic questionnaire that included basic health and developmental questions as well as questions about family language usage patterns. The family language usage questions were used to document language exposure and usage and to ensure that the families and children met the inclusion criterion of speaking Spanish §80% of the time (Kayser, 1989; Kayser & Guiberson, 2008; Mattes & Santiago, 1985). These questions inquired about the percentage of time that the mothers spoke Spanish with their children and the percentage of time that the children spoke Spanish with their parents. If the families and children met the criteria for the study, a study visit was completed within 2 weeks of initial contact. All study visits were conducted in either a parent education room or a child assessment room at the collaborating preschool centers. Parents (either mothers only or mothers and fathers) accompanied their children during the study visits while a Spanish bilingual SLP administered the SPLS±4 and the NWR task. All testing was completed in Spanish. Given the age and cultural background of the sample, we decided to administer the Spanish NWR task using live presentation and active engagement strategies. Of the available studies of Spanish-speaking children, all reported using recorded NWR stimuli; however, all of these studies were with groups of children who were older than those in the current sample. Many of the NWR studies involving English-speaking children that included younger children employed live presentation of NWR items (Chiat & Roy, 2007; Fisher, Hunt, Chambers, & Church, 2001; Gathercole, 1995; Hoff et al., 2008; Stokes & Klee, 2009). Consistent with Chiat and Roy's (2007) active engagement approach to NWR presentation, we used a puppet to present the NWR items. The children were introduced to the puppet and were asked to repeat the puppet's made-up words exactly as the puppet had stated them.
Data Scoring and Reliability Procedures for distinguishing developmental errors from repetition errors and two specific scoring methods were applied. Procedures for scoring errors. A systematic approach was used to score errors. Scoring procedures were developed by Kohnert (2002) in order to distinguish developmental articulation errors related to normal phonological processes from repetition errors. The following scoring procedures were applied:
N N N N N
Each phoneme for PPC scoring, or each item for itemlevel scoring, was scored as correct or incorrect in relation to the target. Phoneme substitutions and omissions were counted as incorrect. Phoneme distortions (productions whose phonetic values deviated from expectations but did not cross phoneme boundaries) were not counted as incorrect. Phoneme additions were not counted as errors because additions do not reflect a loss of information about the target phonemes themselves. When syllable structures were not repeated correctly (i.e., the addition or omission of one or more syllables occurred), individual phoneme scoring was applied after aligning the syllable sequence produced as near as possible to the target and using vowels repeated as syllable anchors.
These procedures for distinguishing developmental articulation errors from repetition errors are based on Dollaghan and Campbell's 1998 scoring approach (Kohnert, 2002). Scoring approaches that allow for developmental articulation errors have been applied to a large body of English (Archibald & Gathercole, 2006; Deevy, Wisman Weil, Leonard, & Goffman, 2010; Dollaghan & Campbell, 1998; Ellis Weismer et al., 2000; Graf Estes et al., 2007; Gray, 2003; Stokes & Klee, 2009) and Spanish NWR studies (Ebert et al., 2008; GutieÂrrez-Clellen & Simon-Cereijido, 2010; Summers et al., 2010; Windsor et al., 2010). Previous research has also shown that children with phonological disorders have no particular disadvantage in repeating lowfrequency nonword sequences when compared to typical peers (Munson, Edwards, & Beckman, 2005). In addition, children's ability to produce nonwords accurately has not appeared to be related to performance on an experimental speech perception task or an informal measure of phoneme production accuracy in real words (Munson et al., 2005). Studies that have described NWR errors in English-speaking (Deevy et al., 2010) and Spanish-speaking children (Ebert et al., 2008) have shown that allowing for developmental articulation errors when scoring NWR items appears to adequately distinguish articulation-related errors from repetition errors. Scoring method 1: Item-level scoring. For the item-level scoring method, a Spanish bilingual SLP scored each item online as a correct or incorrect repetition. The rules described
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earlier for scoring errors were applied to this scoring method. Responses were counted as correct if the repetition included all of the phonemes in the individual nonword. Responses were counted as incorrect if the repetition of the nonword was erred. Errors could have been related to phoneme or syllable deletions or other repetition errors. Allowable developmental errors described in the scoring of errors section were excluded from this consideration. Once all items were scored, the number of correct items was tallied for each syllable length, and the scores for syllable length were summed to calculate the total item-level score. Scoring method 2: PPC. Once again, the rules described earlier for scoring errors were applied to this scoring method. To calculate PPC, individual target phonemes in each nonword were reviewed and were scored as correct or incorrect, taking into account allowable developmental errors described in the scoring of errors section. Once all of the items were scored, the responses were tallied for each syllable length presented, and PPC at each of the five syllable lengths was calculated. In addition, the total PPC was calculated by tallying the total number of correct phonemes produced and then dividing that number by 120 (the total number of phonemes presented). Reliability. The reliability of the two NWR scoring methods was calculated for eight randomly selected children with LI (38% of LI sample) and eight randomly selected TD children (35% of TD sample). Two trained Spanish-speaking graduate students reviewed the recordings to complete reliability coding for both scoring methods. Interrater reliability for item-level scoring was 100% agreement across both groups. Interrater reliability for PPC scoring ranged from 88% to 100% for the LI group and from 94% to 100% for the TD group, with a combined average interrater reliability of 92%. These values are acceptable and comparable to interrater reliability measures reported in other NWR studies.
Results LI and TD Group Comparisons and Descriptions A 2 (group: LI vs. TD) 6 5 (NWR syllable items) mixed analysis of variance (MANOVA) was conducted to assess the effects of LI status and syllable length on repetition accuracy. Age was entered as a covariate and was found to
be significantly related to NWR total scores (p = ,.01). Results indicated a significant effect for language impairment status, F(1, 41) = 5.82, p = ,.05, and NWR syllable length, F (2.74, 112.90) = 8.43, p = ,.001. A nonsignificant LI Group 6 Syllable Length interaction was observed, F(2.74, 112.90) = 2.74, p = .14. An important aim of the current study was to describe how the language status groups (LI and TD) performed on a Spanish NWR task as items increased in syllable length at 3, 4, and 5 years of age. Means and standard deviations by language group, syllable length, and age groupings are presented in Table 3 for item-level scoring and in Table 4 for PPC scoring. Interesting patterns can be detected through visual inspection of these data. Across scoring methods, a general developmental trend was observed, with 4-year-olds outperforming 3-year-olds, and 5-year-olds outperforming 4-year-olds. In addition, as the nonwords increased in syllable length, the children demonstrated more difficulty. Across both scoring methods, the LI group had more difficulty with longer items, especially items that were three, four, and five syllables in length. These results, combined with findings from studies of school-age Spanish-speaking children that included NWR items that were five syllables in length, provided motivation for classification accuracy analyses, specifically evaluating the 3-, 4-, and 5-syllable items.
Classification Accuracy Discriminant analysis is used to predict a categorical criterion variable, such as pass or fail, from multiple independent variables (Leach, Barrett, & Morgan, 2005). Two sets of discriminant analyses were completed to assess whether the NWR scoring method (item-level or PPC) and participants' age could distinguish children with LI from TD children. For each model, a discriminant function that maximally differentiated the groups based on the linear combination of NWR score (based on totals from 3-, 4-, and 5-syllable items) and age was used to categorize individual cases as pass or fail. Classification accuracy measures were calculated using the results from the discriminant analyses and 2 6 2 table format calculations including sensitivity, specificity, +LR, 2LR, and corresponding CIs. For the item-level scoring, the overall Wilks' lambda was significant, l = .84, x2(1, N = 42) = 7.99, p , .01, indicating that item-level scores and age discriminated
Table 3. NWR means and standard deviations for 3-, 4-, and 5-year-old children from the TD and LI groups across tasks and for the total item-level score. TD group
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LI group
Task
3-year-olds (N = 6)
4-year-olds (N = 8)
5-year-olds (N = 9)
3-year-olds (N = 7)
4-year-olds (N = 8)
5-year-olds (N = 6)
1 syllable 2 syllable 3 syllable 4 syllable 5 syllable Total item-level score
3.50 (1.23) 3.33 (1.63) 2.33 (1.97) 2.00 (1.89) .00 (00) 11.17 (5.91)
4.00 (.00) 3.87 (.35) 3.12 (1.64) 2.25 (1.49) .75 (1.04) 14.00 (3.85)
4.00 (.00) 4.00 (.00) 3.89 (.33) 2.89 (1.05) 2.00 (1.32) 16.78 (2.28)
3.57 (1.13) 3.14 (1.46) .86 (1.22) .71 (1.50) .00 (00) 8.29 (4.27)
4.00 (.00) 2.50 (1.69) 2.25 (1.75) 1.63 (1.60) .38 (.74) 11.50 (4.75)
4.00 (.00) 3.50 (.55) 3.50 (.55) 2.00 (1.41) .17 (.41) 13.50 (2.35)
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Table 4. NWR means and standard deviations for 3-, 4-, and 5-year-old children from the TD and LI groups across tasks and for the total percentage phonemes correct (PCC) score. TD group
LI group
Task
3-year-olds (N = 6)
4-year-olds (N = 8)
5-year-olds (N = 9)
3-year-olds (N = 7)
4-year-olds (N = 8)
5-year-olds (N = 6)
1 syllable 2 syllable 3 syllable 4 syllable 5 syllable Total PPC score
88% 83% 71% 67% 43% 61%
100% 98% 93% 88% 76% 86%
100% 100% 99% 94% 84% 93%
92% 84% 46% 43% 23% 46%
94% 85% 71% 62% 52% 66%
100% 98% 96% 84% 47% 78%
(30.61) (40.82) (40.94) (40.68) (38.36) (37.06)
(.00) (4.59) (13.87) (11.61) (20.70) (12.40)
between the children in the two groups. Fifteen of the 21 children with LI were correctly identified (sensitivity of 71%), and 17 of the 23 TD children were correctly identified (specificity of 74%). The +LR for item-level ±scores was 2.74 (95% CI = 1.31±5.73), and the 2LR was .39 (95% CI = .19±.79). For the PPC scoring, the overall Wilks' lambda was also significant, l = .83, x2(1, N = 44) = 8.12, p , .01, again indicating that PPC scores and age discriminated between the children in the two groups. Ten of the 21 children with LI were correctly identified (sensitivity of 48%), and 18 of the 23 TD children were correctly identified (specificity of 78%). The +LR for PPC scores was 2.19 (95% CI = .89±5.36), and the 2LR was .67 (95% CI = .42±1.06). Given that the item-level scores of 3-, 4-, and 5-syllable NWR items resulted in fair discriminant accuracy and moderately strong +LRs and 2LRs, posttest probability was computed (for a review, see Dollaghan, 2007). A positive posttest probability is the probability that a child with LI was found positive for LI after the results from the test were obtained. Bayes' theorem provides a method to calculate posttest probabilities using LR values and pretest probability values (Battaglia et al., 2002). For the current study, a Bayesian calculator was used that provides pretest probability and positive posttest probability coefficients (University of British Columbia, 2012). The pretest probability for the current sample was 48%. The positive posttest probability of NWR item-level scored items was 71%, indicating that there is a 71% probability that children with LI will score poorly on item-level scored 3-, 4-, and 5-syllable NWR items. These results are consistent with the discriminant accuracy measures and indicate that item-level scored NWR tasks may assist in indicating when Spanishspeaking preschoolers have LI.
Discussion The aims of this study were to (a) describe and compare how preschool-age Spanish-speaking children with and without LI perform on NWR across item-level and PPC scoring approaches, and (b) to contrast the classification accuracy of a Spanish NWR task when item-level and PPC scoring methods are applied.
(.00) (.00) (1.66) (6.61) (12.27) (5.56)
(18.89) (37.06) (32.86) (38.21) (23.87) (27.81)
(17.67) (34.67) (37.72) (37.52) (31.86) (32.09)
(.00) (3.61) (3.43) (13.89) (23.78) (9.36)
Group Performance on NWR Across Scoring Approaches Across both item-level scoring and PPC scoring approaches, a developmental trend was observed with both groups of children (LI and TD), with older children outperforming younger children. We also compared the item-level scores of an LI and a TD group of Spanishspeaking children and found that the children with LI performed significantly more poorly than the TD children did. The significant difference between the LI and TD group is a promising result, suggesting that NWR item-level scores tapped into group differences in language skills. Our results and earlier Spanish NWR studies indicated that children with LI have difficulty with NWR, especially with items that are three to five syllables in length (Girbau & Schwartz, 2007; Windsor et al., 2010). Longer syllable items were also more difficult than shorter syllable items, with the 5-syllable items being the most difficult. It was expected that longer items would be more difficult, as they likely begin to exhaust children's phonological memory capacity. Two studies reviewed (GutieÂrrez-Clellen & Simon-Cereijido, 2010; Summers et al., 2010) used an NWR task that included items that were one to four syllables in length. Neither study made mention of a ceiling effect with NWR items, but in one study, a high percentage of children were able to repeat 4-syllable nonwords (Summers et al., 2010), and both research teams recommended that future research include longer NWR items. Five-syllable items may be critically important in detecting subtle differences in NWR in Spanish-speaking children.
NWR Classification Accuracy To contrast scoring methods and evaluate the usefulness of a Spanish NWR task in identifying preschool-age Spanish-speaking children with LI, classification accuracy measures were completed as a final step. The two scoring methods we applied yielded very different classification accuracy values. Item-level scoring yielded adequate sensitivity (71%) and specificity (74%), with moderately +LR and 2LR and corresponding CI ranges that did not include uninformative values. PPC scoring yielded unacceptable sensitivity (48%) and adequate specificity (78%), with +LR
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and 2LR that were weaker than the item-level scoring and CI ranges that spanned into uninformative values. The differences we observed between item-level and PPC scoring of an NWR task may be a result of the fact that for itemlevel scoring, credit is given to children only when entire NWR items are repeated correctly, whereas PPC scoring assigns partial credit to items that are produced with errors (Graf Estes et al., 2007). In this way, item-level scoring is more stringent than PPC scoring. We reviewed three Spanish NWR studies with schoolage children that demonstrated adequate precision and variability (GutieÂrrez-Clellen & Simon-Cereijido, 2010; Kohnert et al., 2006; Windsor et al., 2010). All three studies applied a PPC scoring approach and had good specificity but less than desirable sensitivity. When we employed a PPC scoring approach to our study, we obtained comparable results (good specificity but inadequate sensitivity). Unlike the previous studies, we applied an item-level scoring approach that resulted in improved classification accuracy values. These results provide preliminary evidence that an item-level scoring approach yields better results than a PPCscored approach when applied to Spanish NWR measures. The improved classification accuracy achieved also indicates that an item-level scored Spanish NWR measure may provide information that is suggestive of LI, and with additional sources of information, Spanish NWR measures may assist in indicating LI status. These findings are important because they indicate that item-level scoring yields more accurate results than PPC scoring. The results from the current study are unique because the sample in our study was composed of preschool-age Spanishspeaking children with and without LI, whereas previous classification accuracy studies examined school-age children. Moreover, the current study's results are distinct because they indicate that live administration and active engagement strategies yield results that are consistent with studies of preschool-age English-speaking children. Active engagement and other play-based strategies have been described as developmentally appropriate ways to involve young children in tasks that otherwise may be unappealing (American SpeechLanguage-Hearing Association, 2008; Sandall, Hemmeter, Smith, & McLean, 2005). Based on our experiences with NWR tasks and the results we obtained in the current study, we believe that the use of active engagement strategies likely enhanced the children's attention and willingness to engage in the NWR task; however, this assumption needs further evaluation in future studies. Nonetheless, these findings are important because they indicate that three clinically practical strategiesÐlive administration, active engagement, and itemlevel scoringÐcan be applied to NWR measures and still result in desirable levels of classification accuracy.
Conclusions The results obtained from this study have direct clinical implications: Clinicians can use Spanish NWR tasks that include 3- to 5-syllable items as one of their measures to identify LI in Spanish-speaking preschoolers. Of course, more information (e.g., language samples, behavioral and
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observational measures in authentic contexts, and/or parent report) combined with a Spanish NWR task would be needed to identify LI in preschool-age Spanish-speaking children. The use of multiple data sources is compatible with recent assessment recommendations for children from linguistically diverse backgrounds (Guiberson, 2009; Oetting, Cleveland, & Cope, 2008). There is also evidence from a study of NWR in English speakers with LI that combining NWR measures with other clinical markers results in improved classification accuracy of LI and TD learners (Poll, Betz, & Miller, 2010). We believe that NWR is a promising measure that clinicians can include as one of their multiple data sources to establish LI status in Spanish-speaking children. Our results also indicate that item-level scoring is more effective than PPC scoring in differentiating between LI and TD learners. This is practically significant because of the differences in the effort and time required of item-level and PPC scoring approaches. Item-level scoring is live, immediate, time efficient, and more practical than PPC scoring. An item-level scored Spanish NWR measure can easily be combined with other sources of data to indicate LI status in Spanish-speaking children. Additional research is needed, however, to replicate these findings with young Spanish-speaking children, as well as with bilingual children, with and without LI. Carefully conducted studies with larger samples should be completed as a next step toward establishing the classification accuracy of Spanish NWR tasks with children from a variety of Spanish and Spanish±English bilingual backgrounds. This is especially important given findings from school-age children that indicate that language background and history influence NWR performance. Finally, future studies should compare live presentation and active engagement administration of NWR items to static delivery (e.g., prerecorded stimuli with no play or pretend component). Contrasting these approaches will help determine if there are indeed advantages associated with either delivery approach. The findings of this study add to the existing body of research describing NWR skills in Spanish-speaking children with and without LI. Our results indicate that the ability to repeat nonwords follows a developmental pattern in Spanish-speaking preschoolers, with younger children having more difficulty with NWR, especially with longer items. Children with LI also had significantly more difficulty with NWR when compared to their TD peers. A Spanish NWR task administered with active engagement strategies and scored using item-level scoring yielded classification accuracy values that were suggestive but insufficient to diagnose LI. When combined with other sources of diagnostic information, an item-level scored NWR task with items that were three to five syllables in length may provide helpful information when making decisions about the language status of preschool-age Spanish-speaking children.
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Language, Speech, and Hearing Services in Schools N Vol. 44 N 121±132 N April 2013
Classification Accuracy of Nonword Repetition When Used With Preschool-Age Spanish-Speaking Children Mark Guiberson, and Barbara L. Rodríguez Lang Speech Hear Serv Sch 2013;44;121-132; originally published online Nov 27, 2012; DOI: 10.1044/0161-1461(2012/12-0009)
This information is current as of April 30, 2013 This article, along with updated information and services, is located on the World Wide Web at: http://lshss.asha.org/cgi/content/full/44/2/121
