Pearls index?

Ans. is 'a' i.e., Per 100 woman years Pearl indexo Contraceptive methods are evaluated by Pearl indexo Pearl index is "failure rate per hundred women years of exposure (HWY)"Total accidental pregnanciesFailure rate per HWY = ------------------------------------------------------------- x 1200Total months of exposureo In applying the above formula, the total accidental pregnancies shown in the numerator, must include every known conception, whatever its outcome. The factor 1200 is the number of months in 100 yrs.o A failure rate of 10 per HWY would mean that in the lifetime of an average women about one fourth or 2.5 accidental pregnancies would result, since the average fertile period of a women is about 25 yrs.