This is a linkpost for this artifact I built with Claude Opus 5.5. The summary is below.
Sixteen spending opportunities open to any funder, fifteen of them donations, two models of moral weight, and every exponent from 0 to 2. Model 1 counts animals with neurons, and assumes moral weight is proportional to the number of neurons to the power n. Model 2 adds trees, and soil bacteria and archaea, and assumes moral weight is proportional to basal metabolic rate (BMR) to the power m. Neuron counts, metabolic rates, pain intensities and the welfare of soil organisms in each land class are all uncertain inputs.
Low exponents
Effects on soil organisms dominate, and the interventions that change farmland the most per dollar lead. Under model 1, those that decrease farmland lead, with donations to the Good Food Institute (GFI) first, since soil animals, mostly nematodes, are assumed to fare worse on farmland. Under model 2, those that add farmland lead, with Helen Keller Intl's vitamin A supplementation ahead of Giving What We Can (GWWC). Farmland holds fewer soil bacteria and archaea, whose lives are assumed negative in expectation. These leads come from guessed mean welfare levels much smaller than their spreads, and each leader is among the worst options under the other model. So they show which questions research should answer more than which of the interventions analysed to fund.
The leader changes quickly with the exponent. Under model 1, GWWC leads. It moves several dollars per dollar to effective charities, mostly in global health and animal welfare. At these exponents, both the people saved by GiveWell's All Grants Fund and the hens helped by cage-free campaigns matter, and GWWC's pledgers give to both. Under model 2, the Shrimp Welfare Project's (SWP's) Humane Slaughter Initiative (HSI), which electrically stuns shrimps, leads, and comes close under model 1. Its beneficiaries have small weights but may be spared intense suffering at slaughter. Its position turns on whether stunning reduces suffering and on the intensity of excruciating pain.
High exponents
Effects on the target beneficiaries, the people or animals each intervention aims to help, dominate. This favours humans and chickens. Under model 1, a gift to Helen Keller Intl restricted to vitamin A supplementation leads at high exponents, through the children saved and their descendants. Most of the deaths it averts are in Niger and the DRC, where GiveWell estimates low costs per life saved. GWWC comes second at the highest exponents. Under model 2, cage-free campaigns lead, except at the highest exponents, where GWWC does.
Farmland per dollar
Helen Keller Intl's vitamin A supplementation adds the most farmland per dollar on average, through the farmland of the children saved and their descendants. The two interventions that make people eat more beef add less, as a dollar buys little beef: buying canned corned beef made in Brazil, and donating cows to be sacrificed in Brazil at Eid al-Adha through Qurbani Foundation USA. Still, the ranges from the 5th to the 95th percentile of all the interventions adding farmland overlap (farmland per dollar).
Robustness
Few results are robust. Whether soil organisms have negative lives, and whether farming worsens them, are close to coin flips. So at low exponents the sign of most interventions' effects is unclear. At high exponents, the leaders under model 1 have a high chance of a positive effect. Under model 2, they do too. Under model 1, vitamin A supplementation keeps its lead at the highest exponents in every sensitivity analysis. Under model 2, the leader at the highest exponents changes with GWWC's conservative multiplier and without the weighting for uncertainty over time, and the leader just below them changes with Vasco Grilo's pain intensities. Some leads are also statistical ties within the noise of the simulation (using the results).
So which cause to prioritise turns on the form and exponent of the moral-weight function, the welfare of soil organisms, the intensity of excruciating pain, whether stunning reduces suffering, and how many dollars GWWC moves per dollar. Research could narrow all of these (key assumptions).
