You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Contraceptive efficacy is measured by and explain in detail?
Contraceptive Efficacy: Is assessed by measuring the number of unplanned pregnancies that occur during a specified period of exposure and use of a contraceptive method. Two methods used are:

Pearl Index
Life table analysis

Life Table Analysis (LTA) as measure of contraceptive efficacy:
– LTA calculates a failure rate per month of use
– Better measure than PI