On the probability of demonstrating differential fertility in genetic studies.

Computer simulation has been used to investigate the probability of detecting genetic differences in fertility in small cohorts. It was found that in cohorts of size 200 which have the demographic characteristics of females born in the United States in 1921--5, the probability is approximately 0.50 of detecting, by analysis of variance, either a 20% reduction in the monthly probability of conception or a 15--20% increase in the rate of foetal loss in the first month after conception. Consideration is given to the relative sensitivities of various observable measures of fertility to variation in underlying fertility components.