I'm using Stata 15.1 and I'm trying to replicate an example from the UCLA Statistical consulting site.

I copied the following code directly from that site:
global R2ab = ($Vnull - $Vab)/$Vnull

global macros named Vnull and Vab were defined are appear when I issue a macro list command. Stata is returning the following error message:
too few ')' or ']'

Just don't know what's triggering the error message. Thanks.