Appendix 3: Comparison Group Choices for Assessing Impact
Appropriate comparison groups are needed to attribute changes in outcome measures to a major output (or group of outputs). No one comparison group choice is ‘best’ in all situations. Ethical and delivery obligations limit how services get allocated, and may therefore influence your choice of how comparison groups are set up.
Good comparison groups must be similar to the treatment groups in all respects, except with respect to the intervention being tested for effectiveness.
