How valid are measures of beliefs about the causes of illness? The example of myocardial infarction

Abstract

In Multi-Trait Multi-Method (MTMM) studies of causal attributions for laboratory events, there is little evidence of convergent and discriminant validity for attribution measures. We report the first MTMM study to investigate the validity of two methods of eliciting causal beliefs for an illness, specifically, myocardial infarction. Adult respondents (N = 107) listed causes of MI, then completed questionnaire rating scales for causal beliefs for MI. Measures were compared using both Campbell and Fiske's approach to MTMM analyses, and a Confirmatory Factor Analysis approach. Neither single item measures causal beliefs, nor scales of causal beliefs derived using exploratory factor analysis provided much evidence of convergent and discriminant validity. Confirmatory factor analysis showed that a model containing only causal belief factors provided a moderately good fit to the data. Adding a questionnaire method factor significantly improved the fit of the model, as well as substantially changing the pattern of factor loadings: loadings of questionnaire items on causal belief factors were markedly reduced. These results highlight major problems with the measurement of causal beliefs, and in particular question the validity of factor analysis of questionnaire measures of causal beliefs. They also suggest that at least some of the MI causal belief factors reported in the literature are artefacts of common questionnaire method variance.