Use of structural equation modeling to test the construct validity of the SF-36 Health Survey in ten countries: results from the IQOLA Project. International Quality of Life Assessment

Assessment of quality of life in a multicultural cancer patient population

Quality of life (QOL) is increasingly assessed in cancer patients. In this article, the authors examined the psychometric performance of a commonly used QOL questionnaire, the Quality of Life Questionnaire--Cancer 30 (QLQ-C30; N. K. Aaronson et al., 1993), in multiethnic cancer patients. Content validation studies in patients and clinicians identified possible new items. Multiple-group confirmatory factor analysis supported equivalent structure across ethnic groups (Caucasians and Asian/Pacific Islanders [APIs]). A higher order QOL factor appeared to directly affect functioning scales and symptom count. Exploratory factor analysis examined effects of new items. Ten factors were extracted, 6 consistent with the original instrument and 4 reflecting potentially new aspects of QOL: Positive Social Support, Coping, Existential Well-Being, and Sexuality/Intimacy. The QLQ-C30 appears appropriate for use in API cancer patients. Further work needs to ensure that it includes all important domains.

Quality of life in multiple sclerosis: influence of interferon-beta1 a (Avonex) treatment

BACKGROUND

Numerous data argue for initiating treatment with interferon-beta (IFN-beta) at an early stage in multiple sderosis (MS). The consequences of its use may negatively influence the MS patient's quality of life (QoL).

OBJECTIVE

To evaluate the QoL of MS patients before and after a one-year period of treatment with IFN-beta1a (Avonex).

PATIENTS AND METHODS

QoL was assessed using the SF-36 in 121 relapsing-remitting MS patients. We compared QoL before and after treatment and with data from a normal population. We also studied the possible influence of disease progression on the SF-36 scores.

RESULTS

One hundred six patients completed the study (87%). Compared to a normal population, patients were, at baseline, worse off for all QoL scales, varying from a minimum decrease of 0.73 SD in mental health, to a maximum decrease of 1.55 SD in general health. After treatment, we found no significant changes in any of the QoL scores, except for physical function, where we noted a slight but significant decrease (p = 0.03). Furthermore, there was no significant change either in the physical component summary (PCS) or mental component summary (MCS). The 'reported health transition' item was significantly improved compared to baseline (p = 0.001). At indusion, significant correlations were found between EDSS scores and scores of physical function (p < 0.001), role - physical (p < 0.01), general health and social function (both p < 0.01), and with the PCS (p < 0.01). Patients with dinical relapses and/or disability progression had a more significant decease in physical function (p < 0.05) and also in social function (p < 0.05).

CONCLUSION

The QoL, assessed by the SF-36 scale, is correlated with disability in MS. IFN-beta1a treatment (Avonex) has no negative effect on MS patient's QoL.

An interdisciplinary therapeutic approach for dealing with patients attributing chronic fatigue and functional memory disorders to environmental poisoning--a pilot study

Nonspecific symptoms and a general feeling of ill health that is difficult to objectify are the commonest health problems with which patients present to an Environmental Medicine Outpatient Department (OPD). Of this group, a great proportion meets the classification criteria for Chronic Fatigue Syndrome (CFS) or Functional Memory Disorders in association with Idiopathic Chronic Fatigue (FMD-ICF). This is a longitudinal study of the OPD of Environmental Medicine, Freiburg University Hospital, Germany, to determine the feasibility and impact of an interdisciplinary therapeutic approach (self-help program, acupuncture, psychosomatic support by group interventions) in 8 patients with CFS, FMD-ICF, or CFS in association with self-reported Multiple Chemical Sensitivities (sr-MCS). The intervention took into consideration the patients' need for treatment of physical aspects of their disease. This is an important step to motivate patients into required psychosomatic support. Although none of the patients was willing to accept psychosomatic support or psychotherapy at study outset, acceptance of psychosomatic group interventions was high during the study course. Additionally five patients started with personal counseling at the Psychosomatic Clinic, and, without feeling stigmatized, 4 patients started with specific psychotherapy. The patients' quality of life showed no increase after four months, but, as shown by the Sum-Score of SF-36, it had improved significantly at the end of the study, which covered eight months' treatment (p = 0.015). Two follow-up investigations showed that this improvement probably persisted in part (mainly in the dimensions mental health, social function, physical role function, and vitality). In conclusion our interdisciplinary therapeutic approach indicates successful treatment of patients attributing CFS, CFS/sr-MCS, and FMD-ICF to environmental poisoning. We now plan to conduct a randomized controlled trial in the future.

A prospective study of the impact of stress on quality of life: an investigation of low-income individuals with hypertension

The role that major and minor life events play in the quality of life in low-income hypertensives was examined. Participants were randomly recruited from 2 primary care clinics at a public medical center. The study utilized a prospective design. Participants were determined to have hypertension and were being treated with antihypertensive medication prior to and throughout the duration of the study. Participants were administered the Life Experiences Survey and the Weekly Stress Inventory repeatedly during Year 1 to assess major and minor stress, respectively. Participants were repeatedly administered the RAND 36-Item Health Survey during Year 2 to assess quality of life. Usable data were obtained from 183 patients. Analyses revealed that major and minor stress were significant predictors of all measured domains of quality of life, even after age and number of chronic illnesses were statistically controlled. Minor stress contributed uniquely to the prediction of each dimension of quality of life even when age, number of chronic illnesses, and major life events were accounted for. Findings suggest that stress has a significant, persistent impact on the quality of life of low-income patients with established hypertension. These findings extend prior research that has examined the impact of medications on quality of life and suggest that stress needs to be accounted for as well.

[A hospital suited version of the German SF-36 and its psychometric comparison with the original questionnaire]

OBJECTIVES

The application of the Short-Form 36 Health Survey (SF-36) in hospitals is sometimes problematic, because some formulations like "at work" or "at home" in some items are not adequate in a hospital context. To account for this problem, we deleted 23 words like "at work" and "at home" from the SF-36 and generated thus a slightly modified version, the SF-36 m. The present paper deals primarily with two questions: is the SF-36 m well applicable in hospitals and is it still equivalent with the original version?

METHODS

The SF-36 m was applied in more than 300 patients in two different hospitals. In one hospital a randomised design was used to assess the equivalence of SF-36 and SF-36 m before treatment.

RESULTS

The reported high percentages of missing values in four critical scales were no more observed, when the SF-36 m was applied at the end of hospital stays. Only minor differences between SF-36 and SF-36 m with effect sizes < 0.20 were observed, although the scale "physical role function" and especially item 4d showed unexpectedly significantly higher values in the SF-36 m (p < 0.10). Additionally, higher and significant differences were observed between the applications of the questionnaires at home and in the hospital.

CONCLUSIONS

Opposed to the original SF-36 the SF-36 m is well applicable at the end of hospital stays. SF-36 and SF-36 m show only minor differences in the comparison of their equivalence. The application of SF-36 and SF-36 m in hospitals seems to yield more favourable scores of health related quality of life than the application at home.

The SF-36 summary scales: problems and solutions

To determine the accuracy of the SF-36 summary mental and physical health scales in reflecting their underlying subscales using the traditional method of scoring based on factor coefficients derived through principle components analysis and orthogonal rotation. A representative Australian population survey containing the SF-36 was used to obtain factor coefficients from principle components analysis and orthogonal rotation for scoring the physical component summary (PCS) and the mental component summary (MCS) of the SF-36 in the traditional way. In addition two other methods were used to produce coefficients. The first method used maximum likelihood extraction and oblique rotation. The second method fit a structural equation model to the data in a confirmatory factor analysis. The coefficients derived by each of the methods were applied to the data of a second representative population survey. This survey also provided data on physical and mental health status which allowed comparison of the summary scores and underlying subscales according to various health states. Neither of the scoring methods based on the exploratory factor analyses methods (orthogonal and oblique) produced summary scale scores, by age group, that adequately reflected the underlying subscales. When coefficients derived using structural equation modeling were fit to the data in a confirmatory factor analysis the MCS and PCS accurately reflected their underlying subscale scores. They also produced MCS and PCS scores for the various health states as would be expected from the underlying subscales. The traditional methods of scoring the SF-36 summary scales produce results that would not be expected from the underlying subscales. The problem was only corrected by fitting a structural equation model to the data in a confirmatory factor analysis. The results advise caution in the use of the SF-36 summary scales and suggests that alternative methods of developing factor coefficients need to be employed in studies using the SF-36 summary scales.

[Cross-cultural comparison of Conners Scales: Can the US-American factorial structure be replicated on German clinical sample?]

OBJECTIVE

International networks in child psychiatry research increasingly rely on the cross-cultural generalizability of commonly used questionnaire factor structures. The aim of this study is to analyze whether the U.S. factor structure of the Conners Parent Rating Scale (CPRS) can be replicated in a German clinical sample.

METHOD

A German child psychiatry sample of 1394 children children and adolescents was randomly splitted into halves. One sub-sample was used to calculate a German factor model by means of exploratory factor analysis. This model is tested in comparison with he U.S. model constructed according to Conners (1989) in the second sub-sample by means of a confirmatory factor analysis (LISREL 8).

RESULTS

87% of the path relations in the German and U.S.-American models are identical. Both models show limitations with regard to their predictive power. As expected, the goodness of fit indices for the German model are somewhat better than for the U.S. model (GFI = .81; AGFI = .75 versus GFI = .76; AGFI = .71).

CONCLUSIONS

The goodness of fit indices of the CPRS model are less satisfactory than those of other studies on the cross-cultural generalizability of factor structures of dimensional questionnaires (i.e., De Groot et al., 1994). However, this is mainly due to restrictions within the model (no multiple factor loadings). With respect to the cross-cultural generalizability differences were found in the impulsiveness/hyperactivity scale. All other scales could be well replicated.

Quality of data in multiethnic health surveys

OBJECTIVE

There has been insufficient research on the influence of ethno-cultural and language differences in public health surveys. Using data from three independent studies, the authors examine methods to assess data quality and to identify causes of problematic survey questions.

METHODS

Qualitative and quantitative methods were used in this exploratory study, including secondary analyses of data from three baseline surveys (conducted in English, Spanish, Cantonese, Mandarin, and Vietnamese). Collection of additional data included interviews with investigators and interviewers; observations of item development; focus groups; think-aloud interviews; a test-retest assessment survey; and a pilot test of alternatively worded questions.

RESULTS

The authors identify underlying causes for the 12 most problematic variables in three multiethnic surveys and describe them in terms of ethnic differences in reliability, validity, and cognitive processes (interpretation, memory retrieval, judgment formation, and response editing), and differences with regard to cultural appropriateness and translation problems.

CONCLUSIONS

Multiple complex elements affect measurement in a multiethnic survey, many of which are neither readily observed nor understood through standard tests of data quality. Multiethnic survey questions are best evaluated using a variety of quantitative and qualitative methods that reveal different types and causes of problems.

International validation of the CLAU-S quality-of-life questionnaire for use in patients with intermittent claudication

BACKGROUND

Intermittent claudication (IC) occurs in patients with peripheral occlusive arterial disease and results in leg pain after walking a certain distance - the claudication distance. Until recently, no specific questionnaire has been available to measure quality of life in patients with IC.

OBJECTIVES

To validate the Claudication Scale (CLAU-S) questionnaire in patients in France, the UK, Germany and Belgium.

METHODS

Patients completed the CLAU-S questionnaire and provided demographic and clinical data. Pooled data were examined for psychometric and structural validity and test-retest reliability. Structural equation modelling (SEM) was used to confirm that the questionnaire was measuring the causal relationships involved in IC in each of the language groups studied.

RESULTS

Cross-sectional and factor analysis confirmed the validity of the questionnaire in the pooled patient population. Item convergent and discriminant coefficients and internal consistency reliability coefficients met or exceeded standard criteria. Principal component analysis confirmed the factorial structure. The underlying causal relationships in IC were identified using SEM and were consistent in all language groups studied.

CONCLUSIONS

The CLAU-S questionnaire has undergone validation in English, French, German and Flemish and has a very satisfactory validity in these languages.

SF-36 as a predictor of health states

BACKGROUND

There are a number of claims that Medical Outcomes Study Short Form 36 (MOS SF-36) mean scores can be used to discriminate between healthy and nonhealthy persons and determine various levels of health.

OBJECTIVES

The purpose of this study was to evaluate the ability of the SF-36 to predict whether or not respondents reported health problems.

METHODS

We used structural equation modeling (SEM) techniques to evaluate the SF-36 and its ability to discriminate between those who reported health problems or reported physician-determined illness and those who did not in a sample from the 1990 National Survey of Functional Health Status (NHS).

RESULTS

The correlation between physician-determined illness and Physical Health was -.404, resulting in 16.32% shared variance. The correlation between reported health problems and Physical Health was -.360, resulting in 12.96% shared variance. These correlations are markedly lower than those to the eight first-order scales or between Physical and Mental Health (r = .889). Mental Health could not predict physician-determined illness or reported health problems independent of Physical Health.

CONCLUSIONS

The SF-36 is relatively poor at accounting for the health status of respondents. There are significant paths but the variance accounted for in absolute and relative terms is small. Physical Health does a much better job of accounting for general mental health than it does for perceived health problems or physician-determined illness. These findings suggest that the SF-36 may not discriminate well between healthy and nonhealthy groups and that objective measures of health status may be required in conjunction with the use of the SF-36.

Tests of data quality, scaling assumptions, and reliability of the Danish SF-36

We used general population data (n = 4084) to examine data completeness, response consistency, tests of scaling assumptions, and reliability of the Danish SF-36 Health Survey. We compared traditional multitrait scaling analyses to analyses using polychoric correlations and Spearman correlations. The frequency of missing values was low, except for elderly people and people with lower levels of education. Response consistency was high and compared well with results for the U.S. SF-36. For respondents with computable scales in all eight domains, scaling assumptions (item internal consistency, item discriminant validity, equal item-own scale correlations, and equal variances) were satisfactory in the total sample and in all subgroups. The SF-36 could discriminate between levels of health in all subgroups, but there were skewness, kurtosis, and ceiling effects in many subgroups (elderly people and people with chronic diseases excepted). Concerning correlation methods, we found interesting differences indicating advantages of using methods that do not assume a normal distribution of answers as an addition to traditional methods.

The Danish SF-36 Health Survey: translation and preliminary validity studies

This article reports on the Danish translation of SF-36 and discusses the procedures used for translation improvement, translation evaluation, and scale evaluation. We followed the standard procedures of the International Quality of Life Assessment (IQOLA) Project including forward and backward translation, independent assessment of translation quality, assessment of response-choice weighting through visual analogue scale (VAS) investigations, and psychometric testing of the translated questionnaire. We found that backward translation, independent quality assessment, and VAS studies provided useful information for translation improvement. The Danish SF-36 received a favorable translation evaluation by independent rating; however, interrater agreement was low. Preliminary validity studies generally supported the internal consistency and homogeneity of the Danish SF-36, and the questionnaire performed satisfactorily in distinguishing depressive patients from nonpatients. On the basis of this and other studies, we recommend use of the Danish SF-36 in research.

Methods for validating and norming translations of health status questionnaires: the IQOLA Project approach. International Quality of Life Assessment

This article briefly summarizes methods used in the empirical validation of translations of the SF-36 Health Survey. In addition, information about the IQOLA Project norming protocol and 13 general population norming samples analyzed in this supplement is provided.

Differential item functioning in the Danish translation of the SF-36

Statistical analyses of Differential Item Functioning (DIF) can be used for rigorous translation evaluations. DIF techniques test whether each item functions in the same way, irrespective of the country, language, or culture of the respondents. For a given level of health, the score on any item should be independent of nationality. This requirement can be tested through contingency-table methods, which are efficient for analyzing all types of items. We investigated DIF in the Danish translation of the SF-36 Health Survey, using two general population samples (USA, n = 1,506; Denmark, n = 3,950). DIF was identified for 12 out of 35 items. These results agreed with independent ratings of translation quality, but the statistical techniques were more sensitive. When included in scales, the items exhibiting DIF had only a little impact on conclusions about cross-national differences in health in the general population. However, if used as single items, the DIF items could seriously bias results from cross-national comparisons. Also, the DIF items might have larger impact on cross-national comparison of groups with poorer health status. We conclude that analysis of DIF is useful for evaluating questionnaire translations.

The factor structure of the SF-36 Health Survey in 10 countries: results from the IQOLA Project. International Quality of Life Assessment

Studies of the factor structure of the SF-36 Health Survey are an important step in its construct validation. Its structure is also the psychometric basis for scoring physical and mental health summary scales, which are proving useful in simplifying and interpreting statistical analyses. To test the generalizability of the SF-36 factor structure, product-moment correlations among the eight SF-36 Health Survey scales were estimated for representative samples of general populations in each of 10 countries. Matrices were independently factor analyzed using identical methods to test for hypothesized physical and mental health components, and results were compared with those published for the United States. Following simple orthogonal rotation of two principal components, they were easily interpreted as dimensions of physical and mental health in all countries. These components accounted for 76% to 85% of the reliable variance in scale scores across nine European countries, in comparison with 82% in the United States. Similar patterns of correlations between the eight scales and the components were observed across all countries and across age and gender subgroups within each country. Correlations with the physical component were highest (0.64 to 0.86) for the Physical Functioning, Role Physical, and Bodily Pain scales, whereas the Mental Health, Role Emotional, and Social Functioning scales correlated highest (0.62 to 0.91) with the mental component. Secondary correlations for both clusters of scales were much lower. Scales measuring General Health and Vitality correlated moderately with both physical and mental health components. These results support the construct validity of the SF-36 translations and the scoring of physical and mental health components in all countries studied.

Tests of data quality, scaling assumptions, and reliability of the SF-36 in eleven countries: results from the IQOLA Project. International Quality of Life Assessment

Data from general population samples in 11 countries (n = 1483 to 9151) were used to assess data quality and test the assumptions underlying the construction and scoring of multi-item scales from the SF-36 Health Survey. Across all countries, the rate of item-level missing data generally was low, although slightly higher for items printed in the grid format. In each country, item means generally were clustered as hypothesized within scales. Correlations between items and hypothesized scales were greater than 0.40 with one exception, supporting item internal consistency. Items generally correlated significantly higher with their own scale than with competing scales, supporting item discriminant validity. Scales could be constructed for 93-100% of respondents. Internal consistency reliability of the eight SF-36 scales was above 0.70 for all scales, with two exceptions. Floor effects were low for all except the two role functioning scales; ceiling effects were high for both role functioning scales and also were noteworthy for the Physical Functioning, Bodily Pain, and Social Functioning scales in some countries. These results support the construction and scoring of the SF-36 translations in these 11 countries using the method of summated ratings.