[R-meta] Pre-test Post-test Control design Different N

Marianne DEBUE m@r|@nne@debue @end|ng |rom mnhn@|r
Wed Jan 13 09:04:41 CET 2021


I'm conducting a meta-analysis in ecology on a Pre-test Post-test Control design. 
I'd like to use Morris "dppc2" formula (in Estimating effect sizes from pretest-posttest-control group designs , [ https://doi.org/10.1177%2F1094428106291059 | https://doi.org/10.1177/1094428106291059 ] ) in order to take into account the non-independency of the pre-test post-test design. 
This formula applies for paired-observations and depends on the Pre-test Control Mean, Post-test Control Mean, Pre-test Treatment Mean, Post-test Treatment Mean, Pre-Test Control SD, Pre-test Treatment SD, Treatment Sample size nT and Control Sample size nC. 
Some studies have the same pre-test and post-test nT (and nC) because they always sample the same plots. However, so me studies have a different Pre-Test nT and Post-Test nT (and/or pre-Test nC and Post-Test nC), either because of the experimental design of the author of the study (for example 30 Before samples and 60 After samples), or because we have gathered the Before data if they were given for several years using the Cochrane combined group formula ( [ https://handbook-5-1.cochrane.org/chapter_7/table_7_7_a_formulae_for_combining_groups.htm | https://handbook-5-1.cochrane.org/chapter_7/table_7_7_a_formulae_for_combining_groups.htm ] ) (for example, 30 samples taken 2 years before the intervention, 30 samples taken one year before the intervention, and 30 samples taken one year after the intervention, giving 60 samples taken before the intervention and 30 taken after). 

Do you know if it is possible to adapt the formula to take into account a possible difference in nT or nC between the Before and After? 

Best regards, 

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