[R-meta] Meta Analysis of Interaction Effects

[Ying Cheng]

Dear Meta Community,

I hope everyone has enjoyed the summer so far! 

When conducting a meta-analysis, I am wondering about the appropriate way to extract the effect size for an interaction term (e.g., continuous variable x continuous variable or continuous variable x categorical variable) stemming from regressions.  Many studies reported unstandardized coefficients of the interaction terms. However, given they are using different scales, I assume standardized coefficients will be more appropriate (?). If so, is there any way to transform an unstandardized coefficient of an interaction term from regression to a standardized coefficient? Additionally, some studies also reported simple slopes for the independent variable above and below 1 SD of the mean. Would this information be helpful to calculate the effect size for the interaction?

Another related question would be the way to obtain the sampling variance of such an interaction effect. 

Any information or recommended reading will be greatly valued!

P.S. I appreciate a previous post discussing the effect size for an interaction term stemming from 2*2 ANOVA (https://stat.ethz.ch/pipermail/r-sig-meta-analysis/2018-February/000655.html).

Best,
Ying

Ying Cheng, PhD
Associate Professor
Department of Management
California State University, San Bernardino