Impact evaluations can help to design development programmes by comparing different interventions with regard to their effectiveness. For example, poor Kenyans were offered a variety of ways to encourage saving – text message reminders, matching ten or twenty per cent of savings before or after the savings period, and a simple, fake gold coin with a number for each week of the experiment that served as a physical reminder of savings. The intervention that helped farmers save the most by far was, remarkably, the gold coin (Akbas et al., 2016).

The two main drawbacks of impact evaluations are their high monetary costs and the time required for the results to come back. From the beginning of implementation to the results, an impact evaluation generally takes two years to complete, while many take longer. Average 3ie-supported studies cost 400,000 US dollars and last three years.

Hence, not all projects and programmes of an organisation should be evaluated with regard to their impact; only those where the learning potential is the highest.