[R-meta] d_z and d_av effect sizes in metafor

[Zhouhan Jin]

Hello Wolfgang and Rmeta Community,

I always assumed that under pre-post correlation = 0.5, metafor::escal()'s measure = "SMCC" and "SMCRP" referred to in the article below as "d_z" and "d_av" respectively, are equivalent. But that doesn't seem to be the case (see R code below).

Questions: 1- Can they be equivalent under any condition?
                  2- If yes, will their sampling variances then also be equal?
                  3- If no, are there any other two SMC variants that will be equivalent in both effect size and sampling variances under r=0.5?

ARTICLE: https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2013.00863/full

# R code:
library(metafor)
n <- 30
r <- 0.5  # r set to 0.5 for demonstration
mean_pre <- 0
mean_post <- 0.5
sd_pre <- 1
sd_post <- .5

esc_dz <- escalc(measure = "SMCC", m1i = mean_post, m2i = mean_pre,
                 sd1i = sd_post, sd2i = sd_pre, ri = r, ni = n)

esc_dav <- escalc(measure = "SMCRP", m1i = mean_post, m2i = mean_pre,
                  sd1i = sd_post, sd2i = sd_pre, ri = r, ni = n)

Best wishes,

Zhouhan Jin

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