I built this site because I was looking for a way to donate strategically to candidates for U.S. Congress and didn’t find exactly what I was looking for. I wanted something that worked like an index fund, weighting donations to as many candidates as possible based on the competitiveness of the race, and did so transparently, so I could see exactly how much was going to each candidate.

Although the goals of the site are obviously political, there are aspects of it that I thought might interest HN readers:

* the use of a simple mathematical model to determine donation weights

* transparent presentation of donation weights and amounts

* (hopefully) straightforward UX

I’m not much of a web developer or designer, so I'd appreciate any suggestions for improvement! The site was a good excuse for me to play with Elm, which I enjoyed, and to fight with CSS, which I did not.

There’s no backend; the site just computes donation amounts and ships you off to ActBlue to complete the transaction.

The model for weights is pretty simple. There’s a roughly sigmoidal relationship between vote share and win probability, with win probability increasing rapidly in the region around 50% vote share. I fitted this relationship using the outputs from FiveThirtyEight’s 2018 House model; the cumulative distribution function of a t distribution worked pretty well. The weights are just the density of the same t distribution, and represent the relative increase in win probability due to a dollar.

Since FiveThirtyEight’s Congress models aren’t up for 2020, I’m using Cook Political Report ratings for the House as a rough cut, and a (fully Bayesian) model by Cory McCartan for the Senate.