Concerning scale of implementation, what sort of numbers need to be involved?
The necessary size of the intervention group for determining the impact on outcomes will depend upon a number of factors related to your project, among them: the likely magnitude of the impact on specific outcomes (effect size), the type of evaluation design you’re employing, the nature of control variables included in the analysis, and the statistical tests you’ll rely upon. Issues concerning statistical power should be familiar to the evaluation partner.
