Extrauterine pregnancy and contraception.) (Letter))

In a reply to a letter questioning the use of the word "incidence" of ectopic pregnancies it is suggested that a Pearl rate has been confused with "incidence" in citing the incidence of ectopic pregnancies among IUD users based on a study by Vessey et al. The life-table method is the only method which can yield an unbiased estimate of the incidence of a nonrepetitive disease per unit of time when individuals have different durations of exposure to the disease.