If 100 woman experience 20 accidental pregnancies after using a contraceptive method for 2 years each, Pearl index:
Pearl index is defined as the number of "failures of contraception(i.e, accidental pregnancies) per 100 woman-years of exposure (HWY)" Failure rate per HMY = Total accidental pregnancies X 1200 ----------------------------------- Total months of exposure Thus, on entering values given in question, we get 10 as answer. ** A minimum of 600 months of exposure is usually considered necessary before any firm conclusion can be reached regarding the contraceptive efficacy of a method Contraceptive Method Pearl Index (Per HWY) Calender method 24 Coitus interruptus 18 Male condoms 2-14 Female condoms 5-21 Diaphragm 12 Vaginal sponge Parous women Nulliarous women 20-40 9-20 IUCD 1- 5 OCP 0.1- 2.0 Centchroman (Saheli/CHHAYA) 1.83 - 2.84 Sterilization 0.1
0.1 per 100 women years
100 per 1000 woman years
10 accidental pregnancies per 1000 woman years using contraceptives
10 accidental pregnancies per 100 woman years using contraceptives
JIPMER 2017