I'm reviewing Prophet's documentation on the add_regressors method and came across something called a prior.scale, which is explained as Float scale for the normal prior. If not provided, holidays.prior.scale will be used..
I'm looking for information on what this is/ how it effects predictions, and how to assess/tune the values that it is set to.
Usually if you see some type of scale parameter associated with a prior, it's talking essentially about the standard deviation or spread of the prior. In this case, when you're adding a regressor, I'm guessing the prior mean is that the coefficient is equal to 0. The scale parameter is essentially a check on how large of an effect you expect this regressor to have. If you think it should have a relatively large effect, increase it and vice versa. For what it's worth, here's the description for holidays.prior.scale:
Parameter modulating the strength of the holiday components model, unless overridden in the holidays input.
