Estimating parametric fertility models with open birth interval data.

This paper demonstrates the approach of extending "date of last birth" (DLB) techniques to parametric models. Estimators for Coale-Trussell M and m parameters are constructed from open interval lengths. A new procedure was applied to Brazilian census data, producing maps and spatial statistics for "births last year" (BLY) and DLB m estimates in 723 municipalities in Minas Gerais. DLB estimators are less sensitive to sampling error than BLY estimators. This increased precision leads to clearer spatial patterns of fertility control, and to improved regression. This study produced two main points. The first is that parametric fertility models may be estimated from open-interval birth data in straightforward fashion. The second point is that use of DLB data can make a critical difference to the quality of statistical results. DLB data are often available to researchers, but they are seldom used to their full potential. When fertility data are collected in last-birth or open-interval form, the methods expounded in this paper can make significant improvements in the demographic analysis of small samples.