Abstract
Background: Measuring health status is challenging in Mexican Americans and other diverse groups, because most health measurement instruments were developed and tested in English. Thus, it is difficult to determine whether measured health disparities are the result of actual differences or due to measurement error resulting from translation or conceptual differences.
Objectives: The purpose of this study was to test the metric equivalence of the United States (US) Spanish Short-Form-36 Health Survey (SF-36) in a group of elderly Mexican Americans. In addition, the SF-36 scores of elderly Mexican American women in our sample were compared with normed scores for the SF-36 scales in the general population of elderly US women.
Method: Health status was measured by the US Spanish SF-36 in telephone surveys conducted entirely in Spanish. The sample (N = 65) was elderly (mean age 75.3) and primarily female (78%). Most had less than 7 years of education and an annual income below $10,000.
Results: Missing data were negligible, and did not indicate difficulty with particular items. The item response values were well distributed and item response means were generally similar within a scale. Most item correlations were higher with the item's hypothesized scale than with other scales, though some items in the Mental Health, Vitality, and Social Functioning scales were highly correlated with other scales. Internal consistency reliability (Cronbach alpha) was .80 or above on all scales except Social Functioning (.69). SF-36 scale scores were lower in elderly Mexican American women than in elderly women in the general US population.
Discussion: The US Spanish SF-36 was a generally satisfactory measure of health status in a sample of elderly Mexican Americans with little formal education. The performance of some items in the Mental Health, Vitality, and Social Functioning scales warrants further research.
The impending increase in the ethnic and cultural diversity of a growing United States (US) elderly population has prompted a growing interest in assessing health status to determine if racial or ethnic disparities in health persist in old age. Measuring health status, particularly in terms of each individual's rating of his/her own health, is challenging in groups with diverse cultures and languages, because most health measurement instruments were developed and tested in English. Thus, it is difficult to determine whether health disparities measured by those instruments are the result of actual differences or caused by using instruments that are culturally inappropriate for a particular group.
The primary purpose of this study was to evaluate the metric equivalence of the US Spanish Short-Form-36 Health Survey (SF-36) in a group of elderly Mexican Americans. A secondary purpose was to compare the mean scores on each scale of the SF-36 in Mexican American women in our sample with those of women of the same age in the general US population.
Liang (2002) describes a hierarchy of three levels of measurement equivalence. The first level, conceptual equivalence, uses back-translation, focus groups, in-depth interviews, and random probes to establish cultural meaningfulness and sensitivity of instrument items. Once established, the second step is metric equivalence, which involves a detailed examination of item-level descriptive characteristics (frequency distribution, mean, standard deviation), item internal consistency using the correlation of each item to its own scale and to other scales in the survey, scale internal consistency reliability, and exploratory factor analysis. When conceptual and metric equivalence are established, structural equivalence involves an exploration of the causal mechanisms underlying responses in different racial, ethnic, and cultural groups. The focus of this study was metric equivalence, as the instrument developers had already established conceptual equivalence of the translation.