[R-meta] Treating multiple conditions in within-subjects designs

[Nikoletta Symeonidou]

Dear list-members,

We are currently conducting a meta-analysis using a hierarchical three-level model with the metafor package, where the highest level of the hierarchy is “study” (i.e., outcomes nested within studies). We face a challenge with studies that include more than one control condition and we are unsure how to address this issue in within-subjects designs (i.e., same participants in all conditions).
Specifically, several studies use within-subjects designs with more than two control conditions, which leads to multiple comparisons of interest per study (e.g., experimental condition vs. control condition 1, and experimental condition vs. control condition 2). Our main concern is how to account for the dependence that arises when the same experimental condition is used to calculate multiple effect sizes within a single study.
- Does the hierarchical three-level model inherently account for this dependence?
- If not, what strategies would you recommend for appropriately handling such cases (with the metafor package)?

We greatly appreciate any guidance you can provide. Thank you!

Best regards,
Nikoletta Symeonidou (University of Mannheim)