Pearl Index

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. It is a very approximate measure of the number of unintended pregnancies in 100 woman-years of exposure that is simple to calculate, but has a number of methodological deficiencies.

The index was introduced by Raymond Pearl in 1934.^[1] It has remained popular for over eighty years, in large part because of the simplicity of the calculation.