E. Sadoulet and A. de Janvry. FERNI Policy Brief 29. Fondation pour les études et recherches sur le développement international. 08/2011.
http://www.ferdi.fr/uploads/sfCmsContent/html/111/B29.pdf
Impact analysis is all in design and robustness checks. Not everything can be measured for impact. It is consequently better not to do it when it cannot be done well than to do it wrong. Impact analysis is an art, not a mechanical application of methods. Hence, high quality impact evaluation can be very useful to help define priorities for agricultural investment, identify its effectiveness, and assist in improving implementation, if rigorously done when it can be done.