interpreting main effect in random slopes model

[emazel90]

Hi,

I have a model with time at level 1 and person at level 2. I have added random slopes for time which are significant, however when I do this time as a fixed effect is insignificant.

I was wondering how I interpret this? Is time as a main effect insignificant, and if so can I remove it as a fixed effect and keep it only as a random effect?

Thanks

[GeorgeLeckie]

Dear emazel90,

I would keep the time trend in the fixed-part of the model even if the slope is not significant. The fixed-part time trend is such a fundamental part of the model, it would look odd to remove it, even though it is not significant.

Essentially the population mean does not change over time, but persons are presumably on differential trajectories around this flat mean trajectory with some person trajectories sloping upwards, other downwards.

Best wishes

George