Dispersion Index: measuring trend assessment of geographical inequality in health--the example of under-five mortality in the Middle East/north African region, 1980-1994.

A Dispersion Index for the measurement of geographical inequality in the distribution of health status indicators across space and time is proposed. The Dispersion Index is computed independently of the mean and is robust to changes in distributional shape over time. Therefore, the Dispersion Index is shown to possess more desirable statistical properties as compared to the coefficient of variation for assessing trends in the geographical distribution of health status indicators. Application of the Dispersion Index to the 1994 under-five mortality data from the Middle East/North African region shows that regional inequality in the distribution of under-five mortality was reduced by 47% as compared to 1980. Curve-fitting illustrated that the trend in the Dispersion Index values was non-monotonic from 1980 through 1994. We suggest that apart from the World Summit for Children's under-five mortality target for the year 2000, intraregional targets to reduce geographical inequalities in under-five mortality should be specified. We also suggest that changes in the magnitude of the Dispersion Index be used for the assessment of progress made by a region or nation in achieving the specified numerical targets. From a policy perspective, the Dispersion Index has the potential to be useful in the evaluation of specific health strategies designed to reduce intraregional geographical inequality in the distribution of health status indicators within a specified period.