The justifications for these grants tend to use some simple expected value calculation of a singular rosy hypothetical casual chain. The problem is it’s possible to construct a hypothetical value chain to justify any sort of grant. So you have to do more than just make a rosy casual chain and multiply numbers through.
Our approach to making such comparisons strikes some as highly counterintuitive, and noticeably different from that of other “prioritization” projects such as Copenhagen Consensus. Rather than focusing on a single metric that all “good accomplished” can be converted into (an approach that has obvious advantages when one’s goal is to maximize), we tend to rate options based on a variety of criteria using something somewhat closer to (while distinct from) a “1=poor, 5=excellent” scale, and prioritize options that score well on multiple criteria.
We often take approaches that effectively limit the weight carried by any one criterion, even though, in theory, strong enough performance on an important enough dimension ought to be able to offset any amount of weakness on other dimensions.
… I think the cost-effectiveness analysis we’ve done of top charities has probably added more value in terms of “causing us to reflect on our views, clarify our views and debate our views, thereby highlighting new key questions” than in terms of “marking some top charities as more cost-effective than others.”
Worth noting that even GiveWell doesn’t rely on a single EV calculation either (however complex). Quoting Holden’s 10 year old writeup Sequence thinking vs. cluster thinking: