Dear Antonello,
You hit a bug in an internal function of *meta*: subgroup sample sizes
were set to NA for objects generated with metagen().
I fixed this bug in the GitHub version of *meta* (see
https://github.com/guido-s/meta).
You can install this version using the following commands:
install.packages("devtools")
devtools::install_github("guido-s/meta")
Furthermore, I slightly modified your R code (see attachment).
Specifically, you can use arguments 'n.e' and 'n.c' in metagen() to provide
sample sizes.
Best wishes, Guido
--
Dr. Guido Schwarzer
Institute of Medical Biometry and Statistics,
Faculty of Medicine and Medical Center - University of Freiburg
Postal address: Stefan-Meier-Str. 26, D-79104 Freiburg
Phone: +49/761/203-6668
Mail: sc at imbi.uni-freiburg.de
Homepage: http://www.imbi.uni-freiburg.de