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Good point, that sounds plausible - I attempted to capture it in my poll in reply to Ben's but it has so far not reached many people who actually gave to GWWC.

Peter, thanks for writing out your reasons - it's really useful.

I agree the one large donor point is worrying, but you shouldn't set the donations given by the large donor to zero. There's a reasonable chance GWWC recruits another large donor in the next couple of years and you should take account of that.

In fact, because donor size generally follows a power law, the top donor determines the mean, so if you ignore the top couple of large donors, your expectation value is always going to be too low.

The even bigger point is that I think it's extremely conservative to set all future donations to zero. Yes, talk is cheap, so drop out rates could be much higher than we imagine, but as your example shows, to get to the point where the value of future pledges is zero requires extreme pessimism. Like on the order of 98% dropping out within a couple of years. There's no evidence people are dropping out at anywhere near that rate.

Finally, you're only considering downwards adjustments. What probability would you put on GWWC 'optimistic' scenario in the evaluation doc? I wouldn't be super surprised if the leverage ratio turns out to be over 100. Let's say that's a 10% probability. Then the expected leverage ratio is already at least 10, even if I ignore all the other scenarios. Then there's also the impact that results from GWWC that isn't just money moved (e.g. EA movement building), and the fact that funding now also lays the groundwork for long-term growth, which is where most of the expected value lies.

Thanks very much for your comments Peter, it's very useful to know what people's hesitations are. And thanks Ben, for answering! I just had a couple of quick things to add: With regard to the one large donor - having one such actually makes it more likely that we'd attract others than it would have been otherwise. It doesn't just provide evidence that it's possible - it provides us with opportunities for meeting others in similar networks. Indeed, that has already happened. That impact is then partly due to the original large donor rather than separate things we do. But if attracting that original donor was impact down to GWWC, then presumably the impact of other donors coming partly through their help is similarly so. It feels like you're taking that 1:2.3 number at face value, but it's worth bearing in mind that it leaves out a large number of our routes to impact, including, for example, any good done by donations to non-top charities, any good done by people giving to more effective charities than they would have otherwise, and any donations by non-members other than the one. And of course any money given by members in the future. In terms of whether returns are diminishing or increasing, I think the third impact assessment on the fundraising prospectus is probably the most informative thing to read. It seems like at the moment we're experiencing economies of scale rather than diminishing returns. That could be due to things like it being hard to be a very early adopter of something like giving 10%, but it being much easier to make the leap when there are already a whole bunch of people doing it; it could be because it's easier now we've built up a bunch of infrastructure like a good website. Either way, it does seem to be the case.

To expand on this, the difference between core GWWC (and various layers of the core) and marginal GWWC appears to be a fundamental issue here. In response to a long thread in the other post were people were worrying about GWWC's expansion at some point hitting lower than 1:1 fundraising ratios, Peter put it succinctly:

I agree that GWWC's ratio is probably above 1 with a good deal of confidence (though I haven't done the formal math to evaluate how extreme that statement is). But I think the more compelling argument is that expansion funding on the margin may not have a ratio above 1.

And I expanded:

Yes, there's a huge, huge difference between the impact of GWWC existing as a place where people who wanted to pledge 10% of their income to help those living in global poverty could join others in publicly doing so, and the impact of its marginal funded activities now. GWWC existed as that place before The Centre for Effective Altruism was founded around it as an organisation with donors and a budget supporting paid employees. If minimal resources were spent on creating the basic infrastructure, and I don't know if that's so, but if so, then it had a mega high impact ratio. But it seems wrong to use that to justify keeping on spending more money on more employees doing more marginal projects until the impact from the original resource gets "used up."

OK I'll own up. I downvoted in a blip of initial irritation that you hadn't answered my question, just talking more about CEA, making it look like your argument for funding movement-building might (to be direct) be primarily motivated by self-interest as one of GWWC's salaried Directors. I've now retracted the downvote given I've clarified with this comment though it would still be good to see the argument applied to funding things other than further growing CEA.

Maybe Charity Science?