Two Short Instruments Measuring Quality of Life in ...

European Journal of Psychological Assessment, Vol. 20, Issue 4, pp. 299–309 C.M. Plevier et EJPA al.: Empirical 20 (4), ©Study 2004 Hogrefe of Short&QoL Huber Instruments Publishers

Two Short Instruments Measuring Quality of Life in Survivors of a Myocardial Infarction C.M. Plevier1, M.E.A. Stouthard1, M.C. Visser2, D.E. Grobbee3, and L.J. Gunning-Schepers4 1

Institute of Social Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, Department of Neurology, University Hospital Utrecht, Utrecht, 3Julius Center for Patient-Oriented Research, Utrecht University Medical School, Utrecht, 4Academic Medical Center, Amsterdam, all The Netherlands

2

Keywords: Quality of life, short questionnaires, myocardial infarction

Summary: The aim of this study was to validate the use of short, generic, quality-of-life (QoL) questionnaires in a population of myocardial infarction survivors. The feasibility, reliability, and validity of two short questionnaires (the MOS-24 and the COOP/WONCA charts) were evaluated and compared with a long questionnaire (the Sickness Impact Profile). The study population consisted of 99 myocardial infarction survivors some years after the event and 101 referents without a history of heart or brain infarction. The feasibility of the short questionnaires was good. Both instruments covered the most important domains of QoL, similar to the Sickness Impact Profile. In addition, the two short questionnaires measured “pain” and the MOS-24 also covered “vitality.” The MOS-24 had a smaller floor effect than the COOP/WONCA charts. The MOS-24 was shown to be a reliable test. Both short instruments were able to detect between-group differences (especially MOS-24) although at different rates. Convergent validity of the MOS-24 was high compared with the COOP/WONCA charts. In contrast, the discriminant validity of the COOP/WONCA charts was better. The discriminant validity of the MOS-24 was, nevertheless, reasonable. In conclusion, both instruments are suitable for measuring the QoL of myocardial infarction survivors. The multi-item MOS-24 questionnaire however, is slightly preferable. Health-related quality of life (QoL) is being used more and more as an outcome measure in clinical and population studies (König-Zahn, Furer, & Tax, 1993; Anderson, Aaronson, & Wilkin, 1993; Bowling, 1991; Spitzer, 1981; Wiklund, Herlitz, & Hjalmarson, 1989; Caine, Harrison, Sharples, & Wallwork, 1991). QoL instruments can be categorized as domain-specific, diseasespecific, and generic instruments (König-Zahn, Furer, & Tax, 1993). Generic instruments are, by definition, comprehensive and not disease-specific. Comprehensive implies that at least the physical, psychological, and social

domains are covered. Generic instruments are suitable for the comparison of health outcomes across disease stages and diagnostic groups (Essink-Bot, 1995; Ebrahim, 1995). The present study on the psychometrics of generic measures in myocardial infarction (MI) survivors is part of an ongoing “patient-profile project” describing the changes in QoL of various chronically ill patient groups over time (Boer de, 1997; Scholte-op-Reimer, 1999). Several generic instruments have been developed to assess QoL (König-Zahn, Furer, & Tax, 1993; AnderEJPA 20 (4), © 2004 Hogrefe & Huber Publishers DOI: 10.1027/1015-5759.20.4.299

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son, Aaronson, & Wilkin, 1993; Bowling, 1991). They differ with respect to length, content, and outcome modalities. There are single-item and multi-item measures (Essink-Bot, 1995; Nelson & Berwick, 1989; Donovan, Frankel, & Eyles, 1993; Patrick & Deyo, 1989). Although clearly advantageous in terms of administrative practicality, single-item measures and short-form multi-item scales show weaknesses when compared with long-form scales: For example, they are coarser (relatively fewer levels of health), they have a lower score reliability, and they give a more restricted representation of all important domains of a health concept (Nunnally, 1978). In general, single-item measures are less reliable and less valid than multi-item scales (EssinkBot, 1995; Ebrahim, 1995; Stewart, Hays, & Ware, 1988). Nevertheless, to avoid any unnecessary burden, instruments of limited length are preferred in studies of patient populations, provided they measure generic QoL satisfactorily. The instruments used in the abovementioned “patient-profile project” have already been validated in different disease populations. However, the performance characteristics of these instruments, including feasibility, reliability, and validity, may be population-dependent (Essink-Bot, 1995) to a greater or lesser degree. The aim of the current study was, therefore, to validate the use of short generic QoL instruments (MOS-24 and COOP/WONCA charts) in a population of MI survivors. Some studies are performed to validate QoL questionnaires in various patient populations, however, to the authors’ knowledge, MOS-24 and COOP/WONCA charts have not previously been compared with a longer instrument in an MI patient population some years after the event (McHorney, Ware, Rogers, Raczek, & Rachel, 1992; Brown, Melville, Gray, Young, Skene, & Hampton, 2000; Dempster & Donnelly, 2000).

Materials and Methods The study population consisted of 99 MI survivors and 101 referents. All had been participants in the Rotterdam Study: a prospective follow-up study, initiated in 1990, of determinants of disease occurrence and progression in the elderly. The study cohort of this study was defined as all inhabitants aged 55 years and older of one district of Rotterdam (Ommoord), who lived there at a specific point in time and were willing to participate in the study (7987 subjects participated giving an overall response rate 78%). In that study, all participants were initially interviewed at their homes; later they went to the field center for a medical examination. Details of the RotterEJPA 20 (4), © 2004 Hogrefe & Huber Publishers

dam study were published in 1991 (Hofman, Grobbee, Jong de, & Ouweland van den, 1991). Patients who had been admitted to the hospital because of an MI in the previous 6 to 60 months were selected to participate as MI survivors in a longitudinal study on QOL changes. These MI survivors were enrolled in the period 1991–1993. The diagnosis of “MI” was registered if it was reported by the participants and confirmed by their general practitioner and hospital records (Visser, 1996). Referents were matched at baseline by age and gender to the MI group. This reference group did not have a history of MI or stroke. All participants were interviewed twice, with a 1–3 year time interval, on aspects of QoL during home visits by trained interviewers. The longitudinal data of this study have been presented in a separate paper (Plevier, Mooy, Marang-van den Mheen, Stouthard, Visser, Grobbee, & GunningSchepers, 2001). A total of 194 MI survivors were eligible for participation in the study and 176 referents were matched by age and gender. Thirty subjects from each group refused to participate. The response rate at baseline, therefore, was 84.5% and 83.0% for MI survivors and referents, respectively. Twenty-one MI survivors and nine referents died during the study period and 23 MI survivors and 11 referents were lost at the first follow-up. At the second measurement 21 MI survivors and 22 referents refused to participate. Finally, three referents had a MI during follow-up and were excluded from the analyses. This resulted in 99 MI survivors and 101 referents being interviewed at the second measurement (response rate at follow-up measurement was 69.2% and 75.4% for MI survivors and referents, respectively). Only those subjects with complete data on the questionnaires under study were included in the analyses. The percentage of male subjects was 74.7% in the MI survivor group versus 63.5% in the reference group. The mean age for both groups at follow-up was approximately 72 years. The time since MI diagnosis varied from 18 months to 8 years at the second measurement. Since it is known from the literature that the more healthy persons are more likely to respond, the participants of our study are representative for the more healthy long-term survivors of a MI who live in the general population (Hoeymans, Freskens, Bos van den, & Kromhout, 1998).

QoL Instruments Three QoL instruments were used in this study: the MOS-24, the COOP/WONCA charts, and the Sickness Impact Profile (SIP). The MOS-24 questionnaire comprises the MOS-20 questionnaire plus four items selected from the SF-36 (König-Zahn, Furer, & Tax, 1993;


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Table 1. Dimensions and examples of items within a certain dimension of the QoL instruments entered in the study. Instrument

No. Description/Examples items

MOS-24 (Physical) pain

1

Extent of bodily pain in past 4 weeks

Physical functioning

6

Extent to which health interferes with a variety of activities

Role functioning

2

Extent to which health interferes with usual daily activity (e.g., work, housework, or school)

Social functioning

1

Extent to which health interferes with normal social activities (e.g., visiting with friends during the past month)

Vitality

4

Felt energy, pep, vitality during the past month

Mental health

5

General mood or affect, including depression, anxiety, and psychological well-being during the past month

(Current) health perception

5

Overall ratings of current health in general

Physical fitness

1

What was the hardest physical activity you could do for at least 2 minutes?

Feelings

1

How much have you been bothered by emotional problems such as feeling anxious, depressed, irritable or downhearted?

Daily activities

1

How much difficulty have you had doing your usual activities or task, both inside and outside the house, because of your physical and emotional health?

Social activities

1

Has your physical and emotional health limited your social activities with family, friends, neighbors, or groups?

Change in health

1

How would you rate your overall health now compared to 2 weeks ago?

Overall health

1

How would you rate your health in general?

Pain

1

How much bodily pain have you generally had?

Alertness behavior

10

“I have difficulty reasoning and solving problems (e.g., making plans, making decisions, and learning new things)”

Body care and movement

23

“I dress myself, but do so very slowly”

Communication

9

“I communicate only by gestures (e.g., moving head, pointing, and sign language)”

Eating

9

“I eat special or different food (e.g., soft food, bland diet, low-salt, or low-fat foods)”

Emotional functioning

9

“I laugh and cry suddenly for no reason”

Household management

10

“I do less of the regular daily work around the house than I usually do”

Mobility

10

“I stay in one room”

Recreation and pastimes

8

“I go out for entertainment less often“

COOP/WONCA charts (Items concerning the past 4 weeks:)

Sickness Impact Profile (SIP)

Social interaction

20

“I go out less to visit people”

Sleep and rest

7

“I lie down to rest more often during the day”

Ambulation

12

“I do not walk at all”

Kempen, 1992). The original 20-item MOS-questionnaire covers six dimensions: “Physical functioning, role functioning, social functioning, mental health, current health perceptions, and (physical) pain” (König-Zahn, Furer, & Tax, 1993; Stewart, Hays, & Ware, 1988; Konig-Zahn, Furer, & Tax, 1991; Stewart & Ware, 1992). The four SF-36 items cover the dimension “vitality” (Stewart et al., 1988; Ware & Donald Sherbourne, 1992). The dimension scores range from 0–100. Except for the dimension “physical pain,” higher scores indicate

better QoL. Two versions of the MOS-24 exist: an acute version referring to the the previous week and a chronic one referring to the previous month. The chronic version was used in this study. The COOP/WONCA charts were developed to assess the functional health status of patients in primary care settings. The charts cover the dimensions “physical fitness,” “feelings,” “daily activities,” “social activities,” “change in health (two weeks),” “overall health,” and (optional) “pain” (one chart per dimension). The seven EJPA 20 (4), © 2004 Hogrefe & Huber Publishers

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charts are scored on five-point scales (1 = optimal) (König-Zahn, Furer, & Tax, 1993; Weel van & Scholten, 1992; Kinnersly, Peters, & Stott, 1994; Weel van & Rosser, 1991; Weel van, 1993). The levels on the scales are illustrated with pictograms. The standard Dutch version of the revised charts was used in this study (Weel van & Scholten, 1992). The third generic QoL questionnaire, the SIP, was used to assess convergent validity and to evaluate the known-groups validity of the short instruments. This questionnaire was applied as a reference, because it is known to be reliable and valid in MI survivors and it covers a wide range of QoL aspects (Fletcher, Dickinson, & Philip, 1992; Visser, Koudstaal, Erdman, Deckers, Passchier, Gijn van, & Grobbee, 1995). It consists of 136 items describing the impact of ill health on behavior in 12 dimensions. It is a behavior-based measure of sickness-related dysfunction (König-Zahn, Furer, & Tax, 1993; Bowling, 1991; Essink-Bot, 1995; Bergner, Bobbitt, Carter, & Gilson, 1981; Bergner, Bobbitt, Kressel, Pollard, Gilson, & Morris, 1976; Pollard, Bobbitt, Bergner, Martin, & Gilson, 1976). For this study the answer modalities were amended to provide a “yes/no” tick instead of just a “yes” tick for “yes” responses. The dimension “work” was not included in the analyses as most of the participants were over 55 years of age and thus no longer engaged in paid labor. Scores ranged from 0–100, with higher scores indicating worse functioning. The SIP and the COOP/WONCA charts were assessed by means of a face-to-face interview. The MOS-24, in contrast, was self-administered by the respondent during the interview. Table 1 summarizes the dimensions of the three QoL instruments and provides examples/descriptions of the various items.

Data Analysis All of the analyses were performed in the MI-survivors group, except for those to assess known-groups validity. The data presented here were those collected at the second measurement, because the MOS-24 and the COOP/WONCA charts were only administered at that time.

Feasibility Student’s T-tests were conducted to compare the completion times of the instruments under study. A qualitative analysis of the content of the three questionnaires was also performed. Dimensions/items were considered EJPA 20 (4), © 2004 Hogrefe & Huber Publishers

“comparable” if their content was considered to refer to the same QoL domain. The number of missing responses per dimension of the MOS-24 was used as an empirical indicator of the feasibility of the instrument, because the MOS-24 was self-administered. Ceiling/floor effects of the MOS-24 and the COOP/WONCA charts were evaluated by comparing the percentage of respondents with the maximal possible or minimal possible score across the instruments.

Reliability The reliability of the MOS-24 dimensions (with the exception of the dimensions “pain” and “social functioning,” which consist of just one item) was studied on the basis of homogeneity figures (i.e., Cronbach’s α). Homogeneity refers to the statistical coherence of the scale items and is based on the average correlation of the items in a scale (Cronbach, 1951). In general, homogeneity is considered good if α = 0.70 (Streiner & Norm, 1995). Homogeneity could not be calculated for the COOP/WONCA charts because this instrument consists of one item per dimension. Data on test-retest reliability are not available, because the MOS-24 and the COOP/WONCA charts were assessed at follow-up only.

Validity Known-groups validity, convergent validity, and discriminant validity were assessed in order to evaluate the validity of the instruments. To evaluate the discriminative power of the shortform questionnaires compared to the longer SIP, we tested for differences in scores between MI survivors and referents (known-groups validity). We hypothesized the control sample would have better QoL since they did not endure a MI and so would not have had to cope with the after-effects of this event. Discrimination between the groups can be seen as an aspect of validity since an instrument is valid if it measures differences in functioning. As the scores on the MOS-24 and the SIP were skewed, Mann-Whitney tests were used to examine the QoL differences between MI survivors and referents. Kruskall-Wallis tests were used to detect differences between the groups in the distribution of scores on the COOP/WONCA charts. In order to assess the coherence between the dimensions of the SIP on the one hand and the MOS-24 and the COOP/WONCA charts on the other, we computed a MultiTrait-MultiMethod (MTMM) matrix (Campbell & Fiske, 1959; Schmitt & Stults, 1986). This method enabled us to study the convergent validity (i.e., high


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Table 2. Qualitative comparison of questionnaire content of the SIP, the MOS-24, and the COOP/WONCA charts*. SIP

MOS-24

COOP/WONCA charts

Ambulation Body care and movement Mobility Emotional functioning Social interactions Recreation and pastimes Household management Sleep and rest Communication Alertness Eating – – – –

Physical functioning Physical functioning Physical functioning Mental health Social functioning Social functioning Role functioning – – – – Pain Current health perceptions Vitality –

Physical fitness – Physical fitness Feelings Social activities Social activities Daily activities – – – – Pain Overall health – Change in health (2 weeks)

*This classification of dimensions is used in the analyses of convergent validity

coherence between corresponding dimensions of different instruments) and the discriminant validity (i.e., low coherence between different dimensions within the same instrument) of the MOS-24 and the COOP/ WONCA charts. The SIP was used as a reference (analogous to a criterion in criterion-referenced validity) to assess convergent validity. The classification listed in Table 2 was used in the analyses of convergent validity. The correlation coefficients had to meet four requirements: the first refers to convergence validity, the last three to discriminant validity. (1) Correlation coefficients between tests measuring the same trait assessed with different methods (convergence) should differ significantly from zero and should be high enough to support construct validity. (2) Correlation coefficients between tests measuring different traits assessed by different methods should be lower than those between tests measuring the same trait assessed with different methods. For example, the coefficient between “physical functioning” (MOS-24) and “alertness” (SIP) should be lower than the coefficient between “physical functioning” (MOS-24) and “mobility” (SIP). 3) Convergence coefficients should be higher than correlation coefficients between tests assessing different traits using the same method. For example, the coefficient between “physical functioning” (MOS-24) and “mobility” (SIP) should be higher than that between “physical functioning” (MOS-24) and “vitality” (MOS-24). 4) The pattern of coherence between traits of comparable methods or different methods should be the same. For example, if coefficients between “emotional functioning” and “physical functioning” as measured by the SIP are higher than coefficients between these dimensions and “social functioning” as measured by the SIP, the pattern of

coefficients should be the same for dimensions of the MOS-24. All analyses were performed with the SPSS statistical package (SPSS/PC+, 2001).

Results Feasibility The mean completion time of the MOS-24 and the COOP/WONCA charts was comparable, meanMOS24 (SD) = 6.8 (3.5) min; meanCOOP/WONCA (SD) = 7.9 (10.2) minutes; t(df) = 1.07 (93), p = .29. As expected, the mean completion time of the SIP, meanSIP (SD) = 16.1 (6.0) min, was much longer than that of the short questionnaires, t(df)SIP-MOS24 = –13.8 (92), p < .001; t(df)SIP-COOP/WONCA = –6.5 (92), p < .001. Table 2 presents the qualitative analyses of the content of the MOS-24, the COOP/WONCA charts, and the SIP, and illustrates the comparability of some of their scales. The reader should keep in mind, however, that longer instruments cover specific domains of QoL more extensively. All of the instruments contain unique dimensions of QoL. In contrast to the SIP, the MOS-24 and the COOP/WONCA charts contain the dimensions “pain” and “current health perceptions.” “Vitality” was addressed only by the MOS-24, and “change in health” only by the COOP/WONCA charts. Compared with the referents, the MI survivors often responded “not sure” to items of “health perception” on the MOS-24 (11–22% for MI survivors, 1–16% for referents). This illustrates problems of comprehension with regard to this dimension, especially among MI survivors. EJPA 20 (4), © 2004 Hogrefe & Huber Publishers

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Table 3. Median scores [25th percentile, 75th percentile] of the SIP and the MOS-24 for myocardial infarction (MI) survivors and referents, z value and p value.

MOS-24 Physical functioning Role functioning Social functioning Mental health Current health perceptions (Physical) pain Vitality Sickness Impact Profile Sleep and rest Body care and movement Emotional behavior Household management Mobility Social interaction Ambulation Alertness behavior Communication Recreation and pastimes Eating

MI survivors (n = 99)

Referents (n = 101)

z value

p value

77.8 (55.6–100.1) 100.0 (95.9–100.0) 100.0 (66.7–100.0) 83.3 (69.9– 89.9) 68.0 (65.0– 84.0) 40.0 (20.0– 60.0) 79.2 (66.7– 87.6)

94.5 ( 77.8–100.1) 100.0 (100.0–100.0) 100.0 ( 83.4–100.0) 89.9 ( 79.9– 94.9) 84.0 ( 68.0– 92.0) 20.0 ( 20.0– 60.0) 83.4 ( 75.1– 91.7)

–3.18 –2.25 –3.53 –3.13 –4.98 –2.12 –3.75

0.00* 0.02* 0.00* 0.00* 0.00* 0.03* 0.00*

–3.07 –1.47 –2.60 –1.61 –2.16 –4.25 –1.97 –1.82 –0.63 –3.05 –4.13

0.00* 0.14 0.01* 0.11 0.03* 0.00* 0.05* 0.07 0.53 0.00* 0.00*

10.0 ( 1.0 ( 0.0 ( 7.0 ( 0.0 ( 7.0 ( 7.0 ( 0.0 ( 0.0 ( 12.0 ( 5.0 (

0.0– 0.0– 0.0– 0.0– 0.0– 3.0– 0.0– 0.0– 0.0– 0.0– 0.0–

22.0) 6.0) 10.5) 21.0) 17.0) 16.0) 22.8) 10.0) 0.0) 28.0) 6.0)

0.0 ( 0.0 ( 0.0 ( 0.0 ( 0.0 ( 0.0 ( 4.0 ( 0.0 ( 0.0 ( 0.0 ( 0.0 (

0.0– 0.0– 0.0– 0.0– 0.0– 0.0– 0.0– 0.0– 0.0– 0.0– 0.0–

12.0) 4.5) 0.0) 14.0) 8.0) 9.0) 17.0) 9.5) 0.0) 19.0) 5.0)

*p < .05 Table 4. Distribution of myocardial infarction (MI) survivors and referents over the answering categories of the COOP/WONCA charts and the results of the Kruskal-Wallis analyses.

COOP/WONCA charts Physical fitness MI survivors (%) Referents (%) Feelings MI survivors (%) Referents (%) Daily activities MI survivors (%) Referents (%) Social activities MI survivors (%) Referents (%) Change in health MI survivors (%) Referents (%) Overall health MI survivors (%) Referents (%) Pain MI survivors (%) Referents (%)

Response categories 1 2 3

4

5

9.8 18.9

15.2 23.2

39.1 31.6

20.7 21.1

15.2 5.3

6.5

0.01*

60.9 74.7

18.5 13.7

9.8 6.3

6.5 4.2

4.3 1.1

4.5

0.03*

66.3 82.1

16.3 8.4

10.9 7.4

1.1 2.1

5.4 0.0

6.2

0.01*

81.5 88.4

7.6 5.3

5.4 5.3

5.4 1.1

0.0 0.0

1.9

0.17

4.3 6.3

9.8 6.3

78.3 83.2

7.6 4.2

0.0 0.0

0.10

0.74

6.5 25.3

19.6 28.4

47.8 40.0

20.7 6.3

5.4 0.0

44.6 56.8

28.3 24.2

13.0 14.7

13.0 4.2

1.1 0.0

* p < .05

EJPA 20 (4), © 2004 Hogrefe & Huber Publishers

Kruskal-Wallis (χ²) p value

23.0 3.74

0.00* 0.05


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The number of missing responses on the MOS-24 was small (< 3%). The floor phenomenon for the COOP/WONCA charts was larger than that for the MOS-24: The percentage of MI survivors with the best possible score on the COOP/WONCA charts was, on average, 39% and on the MOS-24 was 30%.

Reliability The homogeneity (Cronbach’s α) of the dimensions of the MOS-24 was reasonable, ranging from 0.59 (“vitality”) to 0.91 (“role functioning”) for MI survivors (see Table 5).

Validity Known-Groups Validity Our analyses showed that all selected instruments were able to detect differences in QoL scores between the groups. Table 3 presents the median scores [25th percentile, 75th percentile] of the MOS-24 and the SIP for both study groups. It shows differences in functioning between MI survivors and referents in all dimensions of the MOS-24 (p < .05). With respect to the SIP, MI survivors were shown to have worse QoL with respect to “sleep/rest,” “mobility,” “social interaction,” “walking,” “emotional functioning,” “recreation and pastimes,” and “eating.” Additional analyses, however, showed that the differences in “eating” were caused by the specific diets frequently seen in subjects with a history of MI (p < .05). Table 4 shows the distribution of MI survivors and referents over the answering categories of the COOP/ WONCA charts and the results of the Kruskall-Wallis analyses. These analyses showed that the MI survivors reported more problems with respect to “physical fitness,” “feelings,” “daily activities,” and “overall health” (p < .05). An MTMM-matrix (Table 5) was calculated using the SIP as reference to assess the convergent and discriminant validities of the MOS-24 (Campbell & Fiske, 1959). As can be seen, the reliability coefficients of the MOS24 are presented on the diagonal. The correlation coefficients of corresponding dimensions (Table 2) were evaluated to assess the convergent validity of the MOS-24. The coefficients were negative (indicating reversed scales), statistically significant, and moderate (–0.45 for SF/SI to –0.72 for PF/AM, Requirement 1). The discriminant validity of the MOS-24 was reasonable since some correlations between different traits assessed by different methods were higher than those between similar traits assessed by different methods (for example: PF/HM:

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–0.59 compared to PF/MO: –0.54 or, for example, SF/SI: –0.45 compared to SF/MO: –0.76, Requirement 2). With respect to Requirement 3, the correlation coefficients of different traits assessed by the MOS-24 were smaller than those of similar traits assessed by the SIP and the MOS-24. Exceptions included SF/RF: 0.73 (MOS-24) compared to SF/SI: –0.45 and SF/RP: –0.65. Finally, the physical functioning dimensions of the MOS-24 and the SIP were associated more with the role functioning dimensions than with the emotional functioning dimensions (Requirement 4). Table 6 presents the MTMM-matrix of the correlation between the COOP/WONCA charts and the SIP. Since the homogeneity of the COOP/WONCA charts could not be computed (the charts consist of only one item), the reliability coefficients have been replaced by a “–.” The correlation coefficients of corresponding dimensions (as hypothesized in Table 2) were evaluated to assess convergent validity. The correlations between corresponding dimensions of the COOP/WONCA charts and the SIP were positive, statistically significant, and small-to-moderate (convergence: 0.30 for SA/RP to 0.65 for PF/AM, requirement one). Except for the social activities chart, these correlation coefficients were higher than the coefficients of different traits assessed by different methods (requirement two). This result and the fact that the coefficients of corresponding dimensions of the COOP/WONCA charts and the SIP were higher than the correlation coefficients of different dimensions of the COOP/WONCA charts (for example, F/EM = 0.54 compared to F/DA = 0.40, etc., requirement three) emphasize the discriminant validity of the COOP/WONCA charts. Another indication of the discriminant validity of the charts is the fact that the physical functioning dimensions of the COOP/WONCA charts and the SIP were correlated more with the role functioning dimensions than with the emotional dimensions (requirement four).

Discussion This study showed that the MOS-24 and the COOP/WONCA charts are valid, reliable, and feasible questionnaires for MI survivors some years after the event. In contrast to the SIP, the questions on these two instruments are stated both positively and negatively, hence, single response tendencies are avoided. Another important advantage of the MOS-24 over the SIP is that the MOS-24 also covers “pain” and “vitality,” domains known to be important to MI patients (Visser, 1996). Although neither short instruments actually assessed “eating,” our data showed that the differences in eating scores between the study groups were based on one quesEJPA 20 (4), © 2004 Hogrefe & Huber Publishers

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tion regarding diet. “Sleep and rest” (a dimension of the SIP for which differences were found between the groups) was not addressed by the short questionnaires, although it did moderately correlate with some of their dimensions. As expected, the SIP measures QoL aspects more extensively: e.g., besides a dimension on “walking,” the SIP contains the dimension “mobility.” This “mobility” scale, however, refers to the social aspects of mobility rather than the physical ones and is therefore less comparable to the physical dimensions of the MOS24 and the COOP/WONCA charts. The dimension scores of the MOS-24 were more balanced than those of the COOP/WONCA charts due to the floor phenomenon of the latter. The COOP/WONCA charts might, therefore, be less responsive than the MOS24. The MOS-24 was also proven reliable. Stewart and colleagues reported similar homogeneity coefficients of the MOS-20 in MI patients (ranging from 0.77–0.88; Stewart et al., 1988). Both short instruments were proven valid. However, the MOS-24 detected differences between MI survivors and referents on more QoL aspects than the COOP/ WONCA charts, implying greater discriminative power. This result is comparable to those of another study that showed a greater impact of several chronic conditions, including MI, on QoL scores when using the SF-36 (an instrument related to the MOS-24) as compared to the COOP/WONCA charts (Beltman, Heesen, Tuinman, & Meyboom-de Jong, 1995). The SIP and the MOS-24 are comparable since the convergent validity was satisfactory. Only the “social activities chart” (COOP/WONCA charts), “social functioning” (MOS-24), and “social interaction” (SIP) corresponded worse than expected, probably because the social dimension of the short questionnaires covers social activities, while “social interaction” (SIP) includes quarrels and isolation. The discriminant validity of the MOS-24 in this study was less than that found in another study (Kempen, 1992), however, that study did not include a specific patient population. These results suggest that discrimination between the dimensions of the MOS-24 decreases when subjects have impaired functioning in more than one dimension. This hypothesis was confirmed in a study of patients visiting a general practitioner’s office, which showed similar coefficients (Stewart et al., 1988). Consistent with previous research, the “health perceptions” scale of the MOS-24 correlated substantially with both “physical” and “mental health.” In fact, that scale correlated with all of the other dimensions of the questionnaire (Stewart et al., 1988; Davies & Ware, 1981). Although our data support the relevant metric qualities of both the MOS-24 and the COOP/WONCA charts in MI survivors, future studies are needed to evaluate EJPA 20 (4), © 2004 Hogrefe & Huber Publishers

their sensitivity to change. These instruments should be assessed in longitudinal studies on changes in QoL that incorporate both clinical and QoL indicators. The SIP, the MOS-24, and the COOP/WONCA charts measure components of health in a different way - actual behavior (SIP) versus subjective evaluation (MOS-24, COOP/WONCA charts). The choice of a particular questionnaire depends on the available resources, the intervention under study, the nature of the population, and the relative importance of the different components of health to the investigator (König-Zahn, Furer, & Tax, 1993; Anderson, Aaronson, & Wilkin, 1993; Bowling, A. 1991; Essink-Bot, 1995; Ebrahim, 1995). Both the MOS-24 and the COOP/WONCA charts are acceptable alternatives in cross-sectional QoL research on MI survivors if the assessment time is limited. The MOS-24, however, is slightly preferable, because it has higher discriminative power, lower floor effects, more resemblance to the SIP, and the advantage of additional dimensions important for MI survivors like “vitality” and “bodily pain.”

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