My mixed effect model design involves assessing 42 different time series via a polynomial function. that is, fixed effects of time and time^2. I've incorporated a random slope of the individual time series.
My hypothesis is effectively does each time series fit a quadratic curve when I allow the coefficients to vary.
My question for here is, is there any issue with incorporating a random effect in this manner. Most documentation assumes multiple time series per random effect and I can't find much on if using it as I have is an issue?