[R-meta] Coding Longitudinal Studies

[Danielle Hiam]

Hello,

I am seeking some clarification on longitudinal studies and coding the random effect using rma.mv.

For context the studies have repeated measures across time and some studies have multiple treatments (exercise in my case). Further, some of the studies have an independent cohort performing the different exercise treatments, others use the same cohort to perform different exercise treatments. I am using the fold change (FC) in expression from baseline for each timepoint and the SEM of the FC. I would like to look at the Fold Change in expression across all cohorts and timepoints and amount of heterogeneity amongst the studies. Then I will investigate with moderators in a meta-regression to investigate sources of this heterogeneity.

I have a couple of basic questions regarding the coding

  1.  Based on my reading I think I would code the random as Time|Study, struct = "AR". This would allow observations from different studies to be independent (Study), but observations from within the same studies be dependent (Time). Is this correct?
  2.  I was also wondering how I code that in some studies they have independent cohorts performing different exercise treatment vs some studies the same cohort performs different exercise treatments.  Would you have a second random effect nesting the groups within each study?
  3.  My last question is regarding the difference in coding the random effect as ~1|Time/Study and ~Time|Study?

Any help or guidance would be greatly appreciated
Kind regards,
Danielle

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