If a woman experiences 2.5 accidental pregnancies after using a contraceptive method, Pearl index:

D i.e. 10 accidental pregnancies per 100 women years using contraceptivesRef: Park, 24th edition, page 544; Principles and Practice of Community Medicine by DrAsma Rahim, 2nd edition, page 439ExplanationPearl index = (Total accidental pregnancies/total months of exposure) * 1200 = * 1200 = 10 per 100 woman years25 years is considered as the average fertile period for a woman for calculation.Contraceptive EffectivenessAssessed by measuring the number of unplanned pregnancies that occur during a specified period of exposure and use of contraceptive method. Two methods are used:Pearl index.Life table analysis.The numerator "total accidental pregnancies" includes all unwanted pregnancies irrespective of the outcome, i.e.,Livebirth.Abortion.Stillbirth; orStill not terminated.DisadvantagesA minimum of 600 months of exposure is necessary for obtaining a valid "failure rate" value.Life table analysis:Calculates failure rate per month of use.More precise than Pearl Index.