Hello All, (1) I want to center my continuous *time* moderator (*time* --> *time_c*) so as to make my intercept meaningful. (2) Because *time* varies both within and between studies, I want to separate the within (*time_within*) and between part of time (*time_between*). I was wondering if I could do both these steps together? If yes, should I first do (1) and then do (2) or vice versa? Have a blessed weekend, Fred
[R-meta] Moderators: Center then separate or vice versa
2 messages · Farzad Keyhan
2 days later
Dear All, I'm doing a meta on the factors influencing the effect of professional development (pd). Each effect estimate in each study may come from: (A) questionnaires with different number of items [`items`], (B) different amount of pd training in hours [`training_hr`], and (C) different amounts of time elapsed up to the point each effect was measured at in weeks [`time_wk`]. For each focal, study-level, categorical moderator (e.g., format of the pd [`pd_format`]), I want to control for A, B, and C across studies. Because A, B, and C can vary both within and between studies, I wonder whether I should control for both their within and between contributions (fit1) or not (fit2)? fit1 <- rma.mv(yi ~ 0 + pd_format + time_wk_whn + time_wk_btw + items_whn + items_btw + training_hr_whn + training_hr_btw, random = ~1|study/obs) fit2 <- rma.mv(yi ~ 0 + pd_format + time_wk + items + training_hr, random = ~1|study/obs) Thank you, Fred