The Pearl Index, also called the Pearl rate, is a technique used in clinical trials for measuring the effectiveness of a birth control method. It is calculated by dividing the number of unintended pregnancies by the number of months of use of the particular method whose efficacy is being measured, and multiplying the result by 1200. It is sometimes used as a statistical estimation of the number of unintended pregnancies in 100 woman-years of exposure (e.g. 100 women over one year of use, or 10 woman over 10 years). It is also sometimes used to compare birth control methods, a lower Pearl index representing a lower chance of getting unintentionally pregnant. In medicine, a clinical trial (synonyms: clinical studies, research protocols, medical research) is a research study. ... Birth control generally refers to any plan or method used to alter or avoid the bodys natural state of fertility, thereby preventing or reducing the probability of pregnancy without abstaining from sexual intercourse; the term is also sometimes used to include abortion and natural family planning. ...

The index is a calculation based on the observations of a given sample population. Thus different studies for the same contraceptive, will give different values for the index.

The index was introduced by Raymond Pearl in 1933. Raymond Pearl (1880-1941) was an American biologist, who spent most of his career at Johns Hopkins University in Baltimore. ... 1933 was a common year starting on Sunday (link will take you to calendar). ...