UndefVarError: @formula not defined

I am using Julia version1.8.5. There was an error " LoadError: UndefVarError: @formula not defined" when I ran "fmla = @formula(outcome ~ GP(X1, X2) | region + covarA + covarB + categ)” in julia. The code and error is showed in the following picture. What should I do to deal with it ? I’ll really appreciated it if anyone can help me out.

You need to actually load a package which defines a @formula macro - judging from your regression specification you might be looking for MixedModels

Thanks for your answer. But there are still few problems that I am confused. First, I don’t know how to find the package which @formula belongs to. Second, besides MixedModels, I also find running “using StatsModels” before using @formula also works, but I don’t know the dfference between MixedModels and StatsModels or other packages including @formula. Which one should I choose. I will appreciated it if you can help to explain it.

How did you know how to write @formula, and how did you know to specify your regression the way you did (ie using the | random effects operator)?

It is true that the are multiple packages which use the @formula macro, StatsModels is the base package defining the @formula DSL but many other packages use and extend it. The question of which one to use can’t be answered on generally, it’s up to you to decide based on the problem at hand, eg got a plain vanilla OLS linear model or probit you might use GLM, if you have high dimensional fixed effects you might use FixedEffectModels, if you want to fit a mixed model then you’re probably interested in MixedModels etc


Thanks for your detailed explanation. It really helps me.