Odstępy inter genetyczne w przekrojowej analizie płodności

Abstract

Real birth intervals are traditionally examined only in the longitudinal approach and in the relation to cohorts and generations. Nevertheless it seems justified to make sometimes several queries:1) what is the time lag between the birth in a given calendar year a of a child of the p-sequence and the previous birth p— l, 2) how much time must pass between the birth p-sequence child na given calendar year a and the p+1 child born later. Such an exposition of the problem seems interesting from at least one point of view: a possibility of analysing the effect of various historical events, related closely to the defined time span, on the length of real birth intervals. Such historical events are war, economic crisis, epidemic of pest, new regulation of abortion. All those events can prolong or shorten the type 1 and 2 intervals in the succeeding calendar years. Currently, frome one year to another, only the type 1 intervals can be traced, while the calculation of the type 2 intervals takes theoretically approximately 30 years, untili the youngest of generations will complete its period of fertility. In practice that period can be substantially shortened. Those problems are not encountered in relation to the deceased populations reconstructed on the grounds of parish registers.