[R-meta] Equivalence of two models in metafor

[Zhouhan Jin]

Dear Wolfgang,

Below, moderator X is coded "no" whenever moderator Y is coded "b" or "c", and moderator X is coded "yes" whenever moderator Y is coded "d".

Thus, I expected that a contrast like "no - yes" (`con1`) to be identical to a contrast like "b + c - d" (`con2`).

However, I wonder why `con1` and `con2` aren't identical?

dat <- read.table(header=TRUE, text="
study  X        Y   yi  vi
1      no       b   1   .1
1      no       b   2   .2
1      no       c   .9  .1
2      no       c   .7  .3
2      yes      d   .6  .1
3      yes      d   .5  .1")

f1 <- rma(yi~X+0, vi, data = dat)
f2 <- rma(yi~Y+0, vi, data = dat)

A = emmprep(f1)
B = emmprep(f2)

( con1 = contrast(A, list(c(1,-1))) )
( con2 = contrast(B, list(c(1,1,-1))) )

Thanks in advance!

Best wishes,

Zhouhan



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