American paternal age data for selected years from 1876 to 1981

For selected years in the time span of 1876 through 1981, mean average paternal ages are itemized and the methods for the calculation of these figures are illustrated. For this time period, mean average paternal ages dropped from a high of 36.9 years to 28.5 years in 1981. This change was accounted for by an absolute and relative decrease in the number of births to older fathers and by an absolute and relative increase in births to younger fathers.