Institutional Learning and Change Initiative

The following text is drawn from the World Bank's website.

Randomization

This technique randomly assigns a pre-determined fraction of the eligible beneficiaries to the project, creating what's called the treatment group. The remaining eligible beneficiaries make up the control group. The difference in outcomes between the treatment and control group is the impact of the project.

Randomization is often the fairest way to allocate beneficiaries to a project if there is insufficient resource to roll out the project to all eligible beneficiaries at once. That is, if the project needs to be phased in to eligible beneficiaries over a number of years due to operational or budgetary constraints, the fairest way to decide who receives the project in the first year is often random assignment. By this method, each beneficiary has an equal chance of receiving the project in the first year.

Source: The World bank http://go.worldbank.org/J35S3J8B60 and http://www.worldbank.org/ieg/ieg_tools.html