When an intervention in a social sector, such as health care or education, shows early positive results, efforts to scale that intervention are not always as successful. This tendency for an intervention to have no effect as it scales is called the “Iron Law” of evaluation. In a recent piece in the Health Affairs Blog, Rocco Perla, Amy Reid, Sandy Cohen, and Gareth Parry discuss four reasons why the “Iron Law” occurs and present how we can reduce its effect.
