Biological performance in beta-thal heterozygotes and normals: results of a longitudinal comparison in a former malarial environment.

Families of beta-thal heterozygotes and of normals studied in 1956 by Silvestroni and Bianco in the small town of Berra near Ferrara were studied again in 1981-85. It was possible to compare mortality, fertility, and migration, in the two groups of heterozygotes and normals after the lapse of one generation. At the power of resolution of the sample available and of the methods used, no difference was visible. However, it was possible to establish the upper limits of the differences in average age at death and in average fertility at the 5% level of significance.