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No-one's going to read this reply, as I'm 13 years too late, but -- oh dear me -- MacKay makes hard work of the medical example.
A straightforward Frequentist solution follows. There are 4 positive cases among the 30 subjects in class A and 10 subjects in class B. We'll believe that treatment A is better if it's very unlikely that, were the treatments identical, there would be so relatively few positive cases among the A's. There are 91390 ways of picking 4 from 40, with only 3810 ~= 4.17% having 0 or 1 in class A. So, unless we were unlucky (4.17% chance) with the data, we can conclude that treatment A is better.
You might find this reference useful: Bayesian Epistemology.
Personal view: if you think you're capable of forming reasonable priors, you're "probably" a Bayesian.
I think my argument is more stark: I'm saying that there are fundamentally two types of credence, (A) and (B) in the comment above, and only one of them is relevant to rational decision-making.
I agree with intuition being the thing that separates Halfers and Thirders, but I'm saying that they're fighting over irrelevant Type (B) credence -- "inner" credence in the OOBR post I linked to.
I've added the Sleeping Beauty tag for you.
Since the rational agent in SBP has full knowledge of the experimental set-up, she has no need of any subjective credence: any bet she takes can be made solely on the facts of the experiment.
Paradoxes like SBP seem to evaporate if you distinguish two types of credence: (A) credence for the experiment that the agent is a part of, vs. (B) credence for the outcomes encountered within the experiment. Type (A) credence for the experimental protocol is all you need for decision-making. Type (B) credence is implied by the experimental protocol and adds nothing to the agent's decision-making capabilities, so you're free to define that however you wish.
See https://www.lesswrong.com/posts/8ecgHXWQBiuY97B2X/ for more detail.
Thank you for the quick reply.
I would agree that having a clear decision objective is important. I would go further: without an objective, why should anyone care how the agent (who, by definition, takes action) feels about their circumstances? I note in your final sentence that you see things differently, but I don't have a killer argument to the contrary.
I can see the need for subjective probability, but only in model selection. Thereafter, you're working to find a strategy maximising the expected value of an objective function. I recorded my thoughts here.
Being new to this, I have no problem asking naïve questions, so: why does Sleeping Beauty need to have any "credence" at all? She's armed with the facts of the experiment and can make decisions based solely on those; why does anyone suppose that she forms some "credence" as a proxy for the facts?
Just like to add that I found your website very clear and, in parts, quite compelling. Thank you.