Achieving better measles immunization in developing countries: does higher coverage imply lower inequality?

Changes in measles immunization are commonly expressed in terms of a change in mean coverage rates but these mean changes may conceal substantial disparities within societies by poverty status. This paper analyzes trends in both the level and the socio-economic distribution of measles immunization coverage in the 1990s for 21 developing countries with two rounds of Demographic and Health Surveys available. We examine these trends using "achievement" indices that combine trends in means and in inequality. We propose and employ "achievement contours" to illustrate graphically how a greater degree of societal aversion to inequality may affect the ranking of countries in terms of achieved measles immunization coverage. The results indicate that most countries have experienced an improvement in their mean measles immunization rate but that this improvement was often unequally distributed across wealth groups, disfavouring the poor in all countries. Mean improvements were found to be associated with both increasing and decreasing inequality. When the trend in the mean and in the degree of inequality was opposite, the trend in the overall "achievement" score is determined by the assumed underlying degree of inequality aversion. As such, the achievement measure "penalizes" coverage improvements that leave the poor lagging behind.