If you are a donor agency, you will receive pamphlets of various types of NGOs for funding requests. The most essential component of that pamphlet would be "case studies of success stories". In fact, one of my batchmates went all the way to Indonesia to document "success stories" of ILO interventions.
In the development world, case studies are preferred over quantitative methods. This is because outcome is as important as output. So you will have "before-after" stories of distressed farmers, widows, and all those of our society who are defined with that derogatory term- "beneficiaries". My strategy Professor, Prof.DPM has a better term. He calls them "community of interest".
Anyway, I was always suspect of such case studies.Many NGOs might just exaggerate benefits provided in order to alleviate donor concerns about how their money is being spent.There are very few donor agencies (SRTT is definitely one) which have a long term approach to poverty alleviation. Most donor agencies are similar to venture capital/private equity investors as far as time horizon is concerned.
I have always been suspect of "claims" made by NGOs. Except large NGOs like BAIF (whose work in Nandurbar I have closely watched for two months), PRADAN, AKRSP and some others, I will always take the "success stories" with a pinch of salt.