WE ARE in a bar, and agree to toss a coin for the next round. Heads, I pay; tails, the drinks are on you. What are your chances of a free pint?
Most people – sober ones, at least – would agree: evens.
Then I flip the coin and catch it, but hide in it the palm of my hand. What's your probability of free beer now?
Broadly speaking, there are two answers: (1) it is still 50 per cent, until you have reason to think otherwise; (2) assigning a probability to an event that has already happened is nonsense.
Which answer you incline towards reveals where you stand in a 250-year-old, sometimes strangely vicious debate on the nature of probability and statistics. It is the spat between frequentist and Bayesian statistics, and it is more than an esoteric problem. "The frequentist-Bayesian debate is the only scientific controversy that actually ...
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