Perhaps there’s some back story to this post that I missed, so forgive me if what I’m about to say has been discussed.
You might consider reading “Superforecasting: The Art and Science of Prediction,” by Philip Tetlock. Or go to the Good Judgment Project web site and watch the 5-part Superforecasting master class.
First, the question has to pass the clairvoyant test. Second, you might want to have some scheme for Bayesian updating your forecast. And then you’ll want to use Brier Scores (or something like them) to assess your accuracy.
If you know R, there’s actually a Brier score function you can use. But I can’t imagine it’s very difficult to set up in Excel.
Again, sorry if I’m stating the obvious.
There are a lot of ways to skin this cat. The most intuitive way I’ve come across is this:
1. If you choose door A, there is a 1⁄3 chance of the prize being behind that door. So there is a 2⁄3 chance that the prize is not behind that door. At this point we distribute the 2⁄3 chance evenly between doors B and C.
2. When the host reveals the the rotten avocado behind, say, door B, then door C picks up the entire 2⁄3 chance of having the prize.
When I apply Bayes’s Theorem to the problem, I essentially get the same thing. The prior probability of the prize being behind door A is 1⁄3, and the posterior probability of it being behind door A is also 1⁄3.