Robust Wagstaff Orderings of Distributions of Self-Reported Health Status

When assessing socioeconomic health inequalities researchers often draw upon measures of income inequality that were developed for ratio scale variables. As a result, the use of categorical data (such as self-reported health status) produces rankings that may be arbitrary and contingent to the scaling adopted. In this paper, we develop a method that overcomes this problem by providing conditions for which these rankings are invariant to the scaling function chosen by the researcher. In doing so, we draw on the insight provided by Alkire and Foster (2004) and extend their method to the dimension of socioeconomic inequality exploiting the properties of Wagstaff’s class of indices. We then provide an empirical illustration using the National Institute of Health Survey 2012.