I have measured the DV and predictor at 2 timepoints in a single group, and am using the MIXED procedure in SPSS. I want to see whether change in the DV over time is predicted by change in the predictor.
Is this specified using an interaction between time*predictor where the predictor is a time-varying or repeated measures predictor variable?
If this is significant, does this say that change in the DV is due to change in the predictor over time? Or is it saying that change in the DV varies based on the overall value of the predictor (same interpretation as a n interaction with a single-timepoint variable)?
From what I have read, the main effect of the predictor simply tells us that the DV is associated with the predictor, and the main effect of time tells us that the DV changes over time, but I need to interaction to look at whether change in the predictor impacts change in the DV over time.