I was unable to quickly find the details of how the UK Institute of Fundraising's studies were conducted. Are there more details somewhere? I'd want to check for survivorship bias, etc.
Also, can I get a page number for the claim pulled from Achieving Excellence in Fundraising?
You're right that the evidence for fundraising is a bit spotty. That's why this project is a trial-run rather than a project for which we're actively seeking funding.
None of us are members of the UK Institute of Fundraising. We don't have enough staff to benefit from their reports and it's not worth the $150 fee. And even if it were, they require one to be fundraising for two years, which we have not done. Therefore we also can't see their methodology and agree that this is suspicious. Though, this report is available.
Additionally "Fund Raising: ...
Many people know about GiveWell and their top-ranked charities. But how easy would it be to make a better one? In "Why It Should Be Easy to Dominate GiveWell's Recommendations", Rob Wiblin notes the simple solution -- fundraise for whatever organizations GiveWell recommends, and raise more than a dollar with each dollar you receive.
Edited on 22 July 2013 to correct a mistaken citation.