Estimating fecundability from data on waiting times to first conception
Heckman, J.J.; Walker, J.R.
Journal of the American Statistical Association 85(410): 283-294
1990
ISSN/ISBN: 0162-1459 PMID: 12155385 DOI: 10.2307/2289763Document Number: 402512
"This article tests assumptions invoked in the demographic literature to estimate the population distribution of fecundability from data on waiting times to first conception. In continuous time, the key assumption is that waiting times are realizations from a mixture of exponentials distribution. In discrete time, the key assumption is that waiting times are realizations from a mixture of geometrics distribution. The [U.S.] Hutterite data analyzed by Sheps (1965) are consistent with this assumption. Various models, however, have one representation in mixture of exponentials form. A fundamental identification problem plagues the conventional estimation procedure. Our analysis calls into question the conventional practice of checking model specification by using goodness-of-fit tests. The practical importance of the identification problem in duration models is demonstrated."