In 2002 in the run-up to the USA’s second invasion of Iraq, when he was challenged about the allegations made by the Bush administration about Iraq’s weapons of mass destruction (WMD) arsenal, Donald Rumsfeld made a memorable logical statement: “The absence of evidence is not evidence of absence. … Simply because you do not have evidence that something exists does not mean that you have evidence that it doesn’t exist.”

A parody of Rumsfeld from the (massively under-appreciated) comic series “The Boondocks”. Warning: coarse language.

In terms of twisted logic, Rumsfeld was right: the fact that intelligence couldn’t find conclusive proof for WMDs in Iraq didn’t necessarily mean they weren’t there; their available methods simply weren’t good enough to find them. But empirically, of course, he was wrong: as we now know, the reason why no proof was found for the WMDs was, they simply weren’t there.

Fast-forward to 2011, to a debate about the evidence for positive impacts of microfinance. Six British researchers recently published an exhaustive study (actually a Systematic Review, S.R.); as I explained on this blog, they pulled together all existing 2,643 publications about microfinance’s impact and looked in depth at the best 58.

Their conclusions – which are too complex and fine-grained to really present in a nutshell – effectively: (1) raised doubts about the research designs used so far, (2) re-iterated that the available evidence could “neither support nor deny the notion that microfinance is pro-poor and pro-women”, and (3) suggested that there has been an “inappropriate optimism towards microfinance”. And finally, they suggested that pursuing microfinance without proof that it works bears the risk of not running other programmes which could work better – opportunity cost. Read the rest of this entry »