Barrett-Marshall - Risk of conception on different days of menstrual cycle

Data about more than 2000 cycles were collected from 241 British married couples who had demonstrated their fertility by the birth of at least one child. Each woman was asked to daily record basal body temperature under domiciliary conditions. Couple also had to keep a record of the occasions on which they had coitus. This kind of data allows to test hypothesis about risk of conception resulting from an act of coitus in different days of the cycle (The days of each cycle have been numbered by negative and positive integers relative to the estimated moment of ovulation, passing from day -1 to day +1 without a day 0). It is also possible to study fecundability in terms of coital frequency.