An impact evaluation is basically a check-up. It measures the effects of a venture and whether or not it reached its goals.

Evaluators use scenarios such as “with versus without” and “before versus after” to gauge impact. For example, a treatment group gets the flu vaccine and a comparison group doesn’t. Who gets sick will make it clear whether the vaccine works.

An impact evaluation also helps answer the question “What next?” If a company’s new mosquito nets are clearly connected to lower levels of malaria in an African village, then scale up the project! But if the evaluation demonstrates that the nets are still faulty, it’s back to the drawing board.