Princeton European Fertility Project
Definition of Fertility Indices

A set consisting of four indexes - If, Ig, Ih and Im - was devised especially for the Princeton European Fertility Project to provide measures that could be easily calculated for most populations given the paucity of data needed to calculate more precise measures.

• I_f = the ratio of the births the women in a given population actually have to the number they would have if subject to a maximal well-recorded age-specific fertility schedule (that of the Hutterites).
• I_g = the ratio of the births the married women in a given population actually have to the number they would have if subject to the maximal age-specific fertility schedule.
• I_h = the ratio of the births the unmarried women in a given population actually have to the number they would have if subject to the maximal age-specific fertility schedule.
• I_m = the ratio of the number of births married women would experience if subject to the maximal age-specific fertility schedule to the number of births all women would experience if subject to that same maximal fertility schedule. This is an index of the extent to which the marital status distribution would contribute to the attainment of maximal fertility in a population in which all births were to marrried women.

The indices have the following relationship:

   If = Im x Ig + (1.0 - Im) x Ih

The indexes were calculated using information from the vital registration systems and from census distributions of the female population by age and marital status; the same type of data and the same procedures were used to calculate the indexes for each province at each date (usually at 10-year intervals). Where it was considered necessary to correct the data for omissions or inaccuracies, this was done. Thus, although the project was extensive in scope and drew on the efforts of many, the indexes are consistent and are as accurate as possible, though errors may remain.