I'm conducting a multilevel regression analysis (mixed model) with time as the levels.
My teacher wanted me to measure time as both a fixed and as a random effect. However, it turned out I couldn't measure time as a random effect because of convergence issues, so it's now only being measured as a fixed effect.
Could someone please explain to me what the consequence is of not measuring time as a random effect? Please use simple language as I'm not a native English speaker and very bad at statistics.
