A New Approach to Modeling Daily Probabilities of Conception
Article first published online: 25 MAY 2004
Volume 55, Issue 4, pages 1005–1013, December 1999
How to Cite
Royston, P. and Ferreira, A. (1999), A New Approach to Modeling Daily Probabilities of Conception. Biometrics, 55: 1005–1013. doi: 10.1111/j.0006-341X.1999.01005.x
- Issue published online: 25 MAY 2004
- Article first published online: 25 MAY 2004
- Received May 1998. Revised February 1999. Accepted March 1999.
- Conception probabilities;
- Fertility models;
- Fractional polynomials;
- Logistic regression;
- Random-effects models
Summary. Standard conception probabilities models assume that different acts of intercourse make independent contributions to the probability of conception in viable cycles. We propose an alternative, approximate model based on the assumption that the act of intercourse closest to the time of maximum fertility is the one most likely to have caused conception. We describe an adaptive algorithm [the most fertile intercourse day (MFID) algorithm] that estimates the most fertile intercourse day in each cycle. The approach is easily extended to include covariates and random between-couple differences in fecundability that affect the probability of conception in a given cycle. Reanalyses of two data sets reported in the literature are presented. Estimates of the probability of conception during the most fertile period of the cycle and of the effects of covariates are similar to estimates found using standard models.