Abstract: Internationally, impact evaluation has become an essential part of program design. However, the challenge on impact evaluation is how to attribute, or how to find out the true impact of program intervention. In general there are two broad types of evaluation methods: non-experimental and experimental. The objectives of this paper are: (1) to briefly compare basic characteristics of each and different evaluation methods, and (2) to discuss in more detail the basic principles and major implementation issues of Randomized Controlled Trails (RCTs). Then the paper uses a current evaluation project of baby nutrition intervention carried out by Rural Education Action Program (REAP) to further elaborate how to evaluate the "true" project impacts using RCTs. Methods belong to non-experimental types include simple comparison of before and after treatment, DID, PSM, IV, RDD, etc. RCT as a rigorous impact evaluation method has its key advantage of avoiding selection bias: the issue that could not be easily solved using other methods. There are five key components in designing an RCT, theory based casual chain analysis to determine what type of interventions in order to achieve target impact, the next is to determine intervention unit and also the way and level of randomizing. A careful examination on likelihood of other factors which may have impact on the outcome should be carefully examined so to be built into intervention design. The last but very important work is to determine project size through power calculation. The implementation of an RCT need to go through "three steps": first is baseline survey, then to randomly assign a group of sample as intervention group while the other half as control group. The last step is evaluation survey. Only with both baseline and evaluation data, one can use then to measure the true impact of project intervention. Like any other methods, RCTs also has its implementation challenges, such as spillover effects, cross contamination, non-compliance or attrition. As a cutting-edge impact evaluation method, Randomized Control Trail (RCT) has a great potential to be widely used in rigorous impact evaluation.

Key words: impact evaluation, Randomized Controlled Trails, Rural Education Action Program(REAP)