Random effects plus a geographic control (e.g. a Gaussian process).

The answer to “fixed or random effects” is pretty much “always use random effects.” If you have more than 2 variables, fixed effects are inadmissible, i.e. always worse (by Stein’s estimator).

There’s really no good reason to use fixed effects for anything, except to save effort.

Random effects plus a geographic control (e.g. a Gaussian process).

The answer to “fixed or random effects” is pretty much “always use random effects.” If you have more than 2 variables, fixed effects are inadmissible, i.e. always worse (by Stein’s estimator).

There’s really no good reason to use fixed effects when you have the option of random effects, unless your goal is to save effort or computation.