How do GiveWell’s funding decisions influence the actions of governments, funders, and other organizations? Answering this question is an important part of figuring out which global health programs are most cost-effective and thus which we should support. We’ve already written about two key factors in our cost-effectiveness estimates: the cost per person reached and the overall burden. But those are only part of the equation.

We also consider what others are likely to do in response to our choices. For example, does our funding displace money the local government had planned to allocate to the program? Or would our funding make other funders more excited to join us in making sure the program is implemented?

Wedding registries provide a loose analogy about how one person’s decision might influence another’s: If someone already bought the toaster on the list, you’re probably not going to buy the lucky couple another one. The money that great-aunt Sally spent on the toaster has displaced the funding you had planned to allocate to the toaster: this is what we call “fungibility.”

In contrast, if the spouses-to-be have signed up for flatware service for 12 and only 6 settings have been purchased, you might prioritize filling out the remainder of the set, to be sure that the couple doesn’t run out of spoons at their upcoming dinner parties. In that case, the guests who purchased the first 6 settings can “crowd in” funding from other guests: this is what we call “leverage.”

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