World Health Organization rates and the av- y erage prevalence of all centers (if more than l in a country) and at the ISAAC center level with local immunization rates. Selected as sociations were examined after control for per capita gross national product (GNP) ob- tained from the World Health Organization Health for All database, 7 over avail- averaged able years from 1980 to 1993. Estimates of effect size were obtained from the univariate. and multivariate normal least squares re- gression when GNP was adjusted for.