I'm trying to run a fixed effects meta-analysis using the Metafor R package and in the documentation I read that it does not return an I^2 for fixed effects models, only for random effects models. This is because the I^2 is calculated using tau^2, which is only computed for random effects models. While the tau^2 is 0 for all the fixed effects models, as it should be, it's giving me non-zero I^2 values.
Does anyone know why it's giving me an I^2 greater than 0 for fixed effects models?
Here's my R macro for the model:
metaFE <- defmacro(data, subset, expr=rma(as.numeric(Beta), sei=as.numeric(StdErr), measure="RR", slab=as.character(study), data=data, subset=subset, method="FE"))
and here is the formula Metafor uses for I^2:
I^2 = 100% × [tau^2 / (tau^2 + s^2)]
Any insight is appreciated! Thanks!