Analysis of Geographic Differentials in Infant Mortality Rates

Comprehensive evaluation of matched infant death certificate data and livebirth certificate data for 1977-1980 was performed for two areas in Israel: Or Yehuda, a small, low socioeconomic status community which had an infant mortality rate of 19.1 per 1,000, and the rest of Ramat Gan district, which had an infant mortality rate of 10.3 per 1,000. A method is presented which illuminates the role of statistical models in analyzing small area data, in evaluating twofold observed differences in crude and factor-specific mortality rates in two areas, in assessing heterogeneity in population stratum-specific mortality rate ratios, and in identifying causes for inter-area differences in infant mortality rate. Identical logistic models were fitted to each of the areas independently, and these were used to investigate effects due to birth weight, sex, parity, maternal age and education, and parental occupation. The differences in the distribution of risk level (number of risk factors) present in each population (or the proportion of multi-problem families) were identified as a single factor that can explain most of the disparity between the areas. The direction and magnitude of the relation between risk level and infant mortality rate were similar in both communities: the greater the number of risk factors, the higher the rate. Identification of a target population for intervention through only one or two specific risk factors would be unprofitable in reducing the overall community infant mortality rate since too many families with multiple risk would be excluded, and too many with single risk factors would be included.