Rigorous impact evaluation is a type of evaluation which has received an increasing level of attention in recent years. It includes randomized or quasi-experimental evaluation designs, and entails the most rigorous statistical analysis of project impacts and the contribution of other factors. The advantage of this type of evaluation is its reliability in terms of being able to identify and attribute the performance of the program or activity being evaluated. But it is also a costly type of evaluation -- a number of rigorous impact evaluations conducted by the World Bank have cost between $200,000 and $900,000 each, depending on program size, complexity and data collection. However, governments such as Chile have conducted this type of evaluation more cheaply, for around $90,000 -- relying on national consultants and, wherever possible, on existing data sets.

Project or program managers who wish to conduct an evaluation of this type are often faced with severe budget, time or data constraints, and these can act as a disincentive to conduct such evaluations. This booklet provides advice for those planning an impact evaluation so they can select the most rigorous methods available within the constraints they face; the various trade-offs between rigor and cost, time and data availability are examined.

This booklet is intended to encourage managers to conduct rigorous impact evaluations when they might otherwise have viewed them as too expensive or time-consuming.

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See also: Impact Evaluation - The Experience of the Independent Evaluation Group of the World Bank