Around this time last year, when my wife and I were looking to give some money to charity, I was struck by a sudden utilitarian panic. I wasn't giving away very much, so how could I know that my small contribution would amount to anything? What if the money just went to some charity's overhead or marketing? Or, perhaps even worse, what if I gave money to a charity that was efficient with its resources but was dedicated to a cause that wasn't the most worthwhile use of my money?

So I asked for help on Twitter. Within a few...