# Theory-Based Impact Evaluation: Principles and Practice

Howard White June 2009 3ie WORKING PAPER 3

Abstract

Calls for rigorous impact evaluation have been accompanied by the quest not just to find out what works but why. It is widely accepted that a theory –
based approach to impact evaluation, one that maps out the causal chain
from inputs to outcomes and impact and tests the underlying assumptions,
will shed light on the why question. But application of a theory-based
approach remains weak. This paper identifies the following six principles to
successful application of the approach: (1) map out the causal chain
(programme theory); (2) understand context; (3) anticipate heterogeneity;
(4) rigorous evaluation of impact using a credible counterfactual; (5)
rigorous factual analysis; and (6) use mixed methods.