Efficacy of Natural Family Planning Methods

There is a difference between effectiveness and efficacy studies involving family planning methods. Efficacy studies determine whether a method works as expected in specified research conditions; effectiveness studies measure how well a method works in real life. The efficacy of a family planning method is usually determined prospectively by studies conducted in a controlled environment. Effectiveness, on the other hand, is based on the unintended-pregnancy rate among a large population of users over time, usually determined retrospectively through chart reviews or surveys. Most studies of NFP are controlled studies—that is, they are efficacy rather than effectiveness studies.