Okay, the scaling issue is was I had assumed then. And thanks for the code. :-)
> As you only compare things alike (eg you wouldn't contrast a main effect (response amplitude) with a time effect)
Yes.
> Let me know if I am overlooking other situations
In some contexts it might be interesting to plot both the amplitude of the average response and the max. change in amplitude over time and possibly, also additively combine them. What I had in mind, say the predictor for average response is a stick function varying between 0 and 1. I had thought (which might well be wrong) that the predictor for a linear time modulation has max. values of 1 and -1 (for the beginning/end of the session) then. Obtaining a beta of 5 for the average and a beta of 3 for the TM would mean the amplitude at the beginning was 8 in beta units and 2 at the end (if onsets exactly matched the beginning/end). If one of the predictors were scaled differently then this would not hold any longer (but could easily be adjusted by multiplying with the required scaling factor, which is a little cumbersome though). But as stated, not sure whether these reflections make sense at all.
Best,
Helmut
|