The Structure of Pregnancy Intervals by Planning Status

Measures of pregnancy intervals are reported for data from the 1975 National Fertility Study in the United States. The structure of such intervals is aggregated into its components by planning status. A measurement model is devised to infer from a survival function some dimensions of the initial distribution of respondents by propensity to experience the event in question. It is adaptable to the study of reproductive intention as well as fecundability and contraceptive effectiveness. The model is applied to the study of the dependence of such behaviour in a given interval on the planning status of the previous pregnancy. Planning status is sequentially well-ordered. Those previously successful with contraceptive use are less likely to fail than those who had previously failed; those who had previously used contraception, whether successful or not, are less likely to fail than those who had not previously used. The credibility of the findings is prejudiced less by the form of model than by the reliability of the basic data.