Analysis of the validity of the vignette approach to correct for heterogeneity in reporting health system responsiveness.

Despite the growing popularity of the vignette methodology to deal with self-reported, categorical data, the formal evaluation of the validity of this methodology is still a topic of research. Some critical assumptions need to hold in order for this method to be valid. In this paper we analyse the assumption of "vignette equivalence" using data on health system responsiveness contained within the World Health Survey. We perform several tests to check the assumption of vignette equivalence. First, we use a test based on the global ordering of the vignettes. A minimal condition for the assumption of vignette equivalence to hold is that individual responses are consistent with the global ordering of vignettes. Secondly, using the hierarchical ordered probit model (HOPIT) model on the pool of countries, we undertake sensitivity analyses, stratifying countries according to the Inglehart-Welzel scale and the Human Development Index. The results of this analysis are robust, suggesting that the vignette equivalence assumption is not contradicted. Thirdly, we model the reporting behaviour of the respondents through a two-step regression procedure to evaluate whether the vignettes construct is perceived by respondents in different ways. Overall, across the analyses the results do not contradict the assumption of vignette equivalence and accordingly lend support to the use of the vignette methodology when analysing self-reported data and health system responsiveness.