Thanks, great question! I can share some data we have from internal surveys and interviews we conducted though this will always be somewhat speculative and personal per founder.

I think it’s good to pull apart the decision to build and to give their wealth away because I think the mechanics and counterfactuals are different.

• You’re right that we are not creating founders from scratch. In our pre-program surveys the median founder put their odds of founding something within three years at ~65–75% even if FTG hadn't existed. So the counterfactual on whether they launch a startup is probably somewhat modest (we're mostly accelerating and de-risking a decision people were already leaning toward). Please note that this is self-reported data - a somewhat smaller subset of participants had already taken steps towards building a startup like quitting their job so we might have made a bit more of an impact here.
• However, there does seem to be a strong counterfactual on the giving. Asked what share of an exit they would have donated without the program, this was roughly 10%, whereas the program mandated a 50% minimum. 
• So why join if you're not already a very committed 50%-giver? 
  • Some of it is likely because people aren't joining for the pledge specifically - but for the accelerator (cofounder matching, the selection signal, structure, community) and accepting the pledge as the entry condition. 
  • But also, interestingly, when we asked our last cohort if the pledge was a positive or a negative reason, the cohort overwhelmingly said it was a positive reason to join (as they believed it would produce a cohort of truly aligned people). I believe only 1 person marked it as a slight negative in their decision.
  • When we asked the cohort more open ended-questions on why people decided to give so generously even when they hadnt considered this before, many of them just said that ‘noone had asked them before’ and ‘upon considering they just realised they weren’t launching this startup for the money anyway’. They also often mentioned the effect of all the others doing the same, and it being attractive to have mutual accountability. 
    
    Hopefully this helps!

Agreed! To get a sense of the success metrics: the total costs of the program were quite lean - we estimate our costs at +-260k pounds in direct costs per cohort, consisting mostly of staff costs and stipends (though I do think these costs might be higher when launched as an independent org because we were able to make use of AIM infrastructure effectively) which means that it would indeed take only 1 successful company to either exit (or achieve a multiple of this in 'direct impact').

Great to hear it's been useful :)