mixed effects meta-regression: nlme vs. metafor
Hi Wolfgang, thanks for the instant and comprehensive reply!
On 01/23/2013 12:39 PM, Viechtbauer Wolfgang (STAT) wrote:
[...] In fact, trying to disentangle that residual variance component from any random study effects is usually next to impossible. I mention this explicitly one more time, because I have seen some publications using lme() in exactly this way ...
I'm not too surprised -- it was only after some double-checking that I noticed that variances are not actually fixed when using the "varFixed" option...
[...] The updated version of the package still does not include that aforementioned function, but I may consider putting a pre-alpha version on the website so that the adventurous are able to try it out.
I'm looking forward to it...!
Alternatively, you could try taking a look at MCMCglmm (http://cran.r-project.org/web/packages/MCMCglmm/index.html), which should be able to fit the model that you want. Can't give you any details on how, but if you get stuck, try posting to R-sig-mixed-models and Jarrod Hadfield (the MCMCglmm package author) is very likely to help you further.
Thanks; I was also thinking of switching to OpenBUGS + R2OpenBUGS, which should provide the necessary flexibility at the price of some extra complication... but having worked with it before, it should be doable... Cheers, Christian