I am running the following model in R:
model = lmer(Tau ~ ageS*days+YrsOfEds*days+sex*days+tract*days + (1|SubjectID), data=long)
With this model I am trying to predict change in tau over time based on the quality of a tract. Both tau and tract are continuous variables (scaled as R complained about the scale... but still is...). Since this is a biological relationship, I have included subjects as random intercept, as this may be different across subjects (I think that my sample size is too small and my time points are too little to test random slopes) Days is also continuous, as this might save me DOF and there is some variability across subjects on when they were exactly tested. We are still collecting data, so far I have 118 subjects for baseline, 32 for follow-up moment 1 and 3 for for follow-up moment 2.
Then I wanted to plot how tau changes over time in relation to tract quality. That seems to be more difficult. I have used sjPlot for that using this command:
(tract and time are modeled as fixed effects, so I thought this was the best option to go for).
I then get this plot:
While this looks great and the effects are in the correct direction, I have trouble understanding this plot. What am I looking at? For example: the HippCing_FAS is the tract quality measure: does this mean that higher values have a low probability of predicting a change in tau?
Any help would be greatly appreciated! Many thanks!!