The Pearl Index, also called the Pearl rate, is the most common technique used in clinical trials for reporting the effectiveness of a birth control method. The total number months or cycles of exposure by women in the study. In the first method, the relative number of pregnancies in the study is divided by the number of months of exposure, and then the pearl study guide pdf by 1200.
In the second method, the number of pregnancies in the study is divided by the number of menstrual cycles experienced by women in the study, and then multiplied by 1300. 1300 instead of 1200 is used on the basis that the length of the average menstrual cycle is 28 days, or 13 cycles per year. It is also sometimes used to compare birth control methods, a lower Pearl index representing a lower chance of getting unintentionally pregnant. Perfect use or Method Pearl Index, which includes only pregnancies that resulted from correct and consistent use of the method, and only includes months or cycles in which the method was correctly and consistently used.
The index was introduced by Raymond Pearl in 1933. It has remained popular for over eighty years, in large part because of the simplicity of the calculation. Like all measures of birth control effectiveness, the Pearl Index is a calculation based on the observations of a given sample population.