Assessing human fertility using several markers of ovulation

In modelling human fertility one ideally accounts for timing of intercourse relative to ovulation. Measurement error in identifying the day of ovulati on can bias estimates of fecundability parameters and attenuate estimates o f covariate effects. In the absence of a single perfect marker of ovulation , several error prone markers are sometimes obtained. In this paper we prop ose a semi-parametric mixture model that uses multiple independent markers of ovulation to account for measurement error. The model assigns each metho d of assessing ovulation a distinct non-parametric error distribution, and corrects bias in estimates of day-specific fecundability. We use a Monte Ca rlo EM algorithm for joint estimation of (i) the error distribution for the markers, (ii) the error-corrected fertility parameters, and (iii) the coup le-specific random effects. We apply the methods to data from a North Carol ina fertility study to assess the magnitude of error in measures of ovulati on based on urinary luteinizing hormone and metabolites of ovarian hormones , and estimate the corrected day-specific probabilities of clinical pregnan cy. Published in 2001 by John Wiley & Sons, Ltd.