Decrement tables, also called life table methods, are used to calculate the probability of certain events.
Birth control
Life table
In actuarial science and demography, a life table (also called a mortality table or actuarial table) is a table which shows, for each age, what the probability is that a person of that age will die before their next birthday ("probability of deat ...
methods are often used to study birth control effectiveness. In this role, they are an alternative to the
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 ...
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As used in birth control studies, a decrement table calculates a separate effectiveness rate for each month of the study, as well as for a standard period of time (usually 12 months). Use of life table methods eliminates time-related biases (i.e. the most fertile couples getting pregnant and dropping out of the study early, and couples becoming more skilled at using the method as time goes on), and in this way is superior to the Pearl Index.
Two kinds of decrement tables are used to evaluate birth control methods. Multiple-decrement (or competing) tables report net effectiveness rates. These are useful for comparing competing reasons for couples dropping out of a study. Single-decrement (or noncompeting) tables report gross effectiveness rates, which can be used to accurately compare one study to another.
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See also
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Survival analysis
Survival analysis is a branch of statistics for analyzing the expected duration of time until one event occurs, such as death in biological organisms and failure in mechanical systems. This topic is called reliability theory or reliability analysi ...
Footnotes
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Birth control
Actuarial science