I am running a longitudinal study (4 measurement periods) and I am looking at what predicts habit formation over time. I put “Time” as fixed effect and I have four predictors that I have placed in random effects. However in my output table “Model Dimension”, I don’t understand why it adds a level to each of the variables in random effects (I get 5 levels- intercept + four predictors). These are all same level predictors I want to test at the same level. For instance, if I added these in fixed effects, they all become grouped in the same level, which is what I want but for random effects. Any insight would be very much appreciated.
If I understand correctly, you have a repeated measures design, but you entered you “time” variable as a fixed factor. If your design involves repeated measures over time then you should be selecting the repeated measures approach in SPSS found in Analyze > general linear model > repeated measures. Enter “time” as a within subjects factor and the number of times people are measured, in this case 4 from what you’ve said. Enter you outcome/dependent variable(s) in “measure name” and click add. Between subjects factors and covariates can be entered in the next window. Good luck.