Perhaps taking a list of registered charities, and weighting their cost effectiveness by their donation revenue would be the most apt way to measure the average cost effectiveness? But I also think that we can only aptly measure the effectiveness of charities that are designed to have measurable effectiveness using RCTs. For charities with no good counterfactual or small sample sizes, quantifying effectiveness becomes impossible. Try measuring the effectiveness of Oxfam as a whole, for example.
Perhaps taking a list of registered charities, and weighting their cost effectiveness by their donation revenue would be the most apt way to measure the average cost effectiveness? But I also think that we can only aptly measure the effectiveness of charities that are designed to have measurable effectiveness using RCTs. For charities with no good counterfactual or small sample sizes, quantifying effectiveness becomes impossible. Try measuring the effectiveness of Oxfam as a whole, for example.