Karlan, Appel, Duflo and Banerjee tackle that question through randomized control trials (RCTs).

FORBES: Book Review: Making Poverty History

Medical research commonly employs three kinds of study designs: observational studies, randomized controlled trials (RCTs), and metaanalyses.

FORBES: Clinical Trial Advice For Investors From Two Pros

Originally designed for the pharmaceutical industry to test the safety and effects of drugs, the authors have pioneered RCTs to test the claims that small, uncollateralized loans to the poor are a persuasive antidote to poverty.

FORBES: Book Review: Making Poverty History

While high-end evaluation methods like randomized control trials (RCTs) are the surest means of determining what interventions in fact cause certain outcomes, they are also time-consuming and costly and beyond the means of many, if not most, mainstream nonprofits.

FORBES: An Interview with Paul Carttar, Director of the Social Innovation Fund