I am conducting a meta-analysis of studies that didn't use a control comparison group. I use metafor on R. I do have the R code for studies with a control but not without a control. My outcome is continuous (0-10 scale). Any help would be much appreciated it. Thank you so much, Mina
You will want to use a mean difference standardized by either the raw score (measure = "SMCR") or the change score (measure = "SMCC"). Raw score standardization involves dividing the difference between the time 1 and time 2 means by the standard deviation of the time 1 scores, while change score standardization involves dividing by the standard deviation of the change scores.
Which one you want to use depends on a couple things.
Is your meta-analysis testing differences across alternate treatments or experimental conditions? If so, the raw score standardization is preferable. If your meta-analysis is primarily concerned with changes in individuals, the change score standardization is better.
Does the test-retest correlation differ substantially across studies? If so, the raw score standardization is preferable, because it doesn't depend on that correlation. In contrast, the effect size based on change score standardization will be increased when the test-retest correlation is high and decreased when the test-retest correlation is low.
See more on this page about how to write the R code to calculate the effect sizes, under Outcome Measures for Change or Matched Pairs -> Measures for Quantitative Variables.
I also highly recommend reading the following paper on this topic: Morris & Deshon (2000).