The Swedish SF-36 Health Survey II. Evaluation of Clinical Validity

Abstract

The validity of the Swedish SF-36 Health Survey was examined, replicating techniques used in the U.S. validation. Principal components analysis was used to test the internal structure of the eight SF-36 scales in relation to hypothesized associations with the two major dimensions of health—physical and mental. Hypothesized relationships between scales and external criteria were also examined by means of clinical group contrasts. Both the principal components analysis and clinical group contrasts largely replicated U.S. findings, which supported the cross-cultural stability of the SF-36 in Sweden. As expected, the Physical Functioning and Mental Health scales were most sensitive to clinical manifestations of medical and mental health, respectively. The General Health scale was associated more with physical than mental health. However, the Social Functioning scale and particularly the Vitality scale were more related to mental health in Sweden than in the corresponding U.S. study. Cultural differences and variation in study samples and selection criteria were suggested as possible explanatory factors for these differences.

Introduction

The development of reliable, valid, and practical outcome measures is an important area of health research. Many generic questionnaires have been developed to assess subjective health status. They commonly include measures of physical, mental, and social health, typically labeled health-related quality of life 1, 2. However, only a few such measures fully satisfy essential criteria such as comprehensiveness, reliability, validity, and cross-cultural applicability and yet are short enough for use in clinical trials and everyday clinical practice. The SF-36 Health Survey seems promising toward this end. Apart from its proven psychometric qualities and practical usefulness 3, 4, 5, 6, 7, the SF-36 deserves consideration because of the multinational testing now accomplished through the IQOLA Project 8, 9, 10, 11, 12, 13, 14, 15.

The theoretical constructs that guided the development of the SF-36 were the two major dimensions of health—physical and mental—found in several empirical studies 5, 7, 16. Thus, a major goal in the construction of the eight primary scales included in the SF-36 was to capture these two dimensions in order to separate health problems mainly of a physical character from problems mainly of a mental character or a mixture of these two. The purpose of the present study was to collect further evidence of the construct validity of the Swedish SF-36. Specifically, the objectives were (1) to test if the eight scales psychometrically are related to these two dimensions in the expected direction; (2) to assess the extent that the scales differentiate between groups of subjects that should differ in the hypothesized constructs according to external criteria (known groups analysis). Both of these aspects of construct validity have also been examined for the original U.S. version of the SF-36 [5]. To facilitate comparisons and meet the standards for validation in the IQOLA Project, we followed closely the methodology used in that study.