title: Estimating fecundability from data on waiting times to first conception.
abstract: "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."
authors.forename: J J
authors.initials: JJ
authors.lastname: Heckman
authors.forename: J R
authors.initials: JR
authors.lastname: Walker
mesh_terms: D000569:Americas; D001723:Birth Rate; D003710:Demography; D019049:Developed Countries; D005069:Evaluation Studies as Topic; D005298:Fertility; D008962:Models, Theoretical; D009656:North America; D011153:Population; D011157:Population Dynamics; D011158:Population Growth; D012098:Reproduction; D012106:Research; D013997:Time Factors; D014481:United States
keywords: Americas; Demographic Factors; Developed Countries; Evaluation; Fecundability; Fecundity; Fertility; Fertility Measurements; High Fertility Population; Models, Theoretical; North America; Northern America; Population; Population Dynamics; Reproduction; Research Methodology; Time Factors; United States