mixed modelling with random effects with different correlation structures? GLMM/GEE mix
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On 13-10-01 10:04 AM, R.Klink, van wrote:
Dear Prof. Bolker I write you on behalf of my colleagues working in the same project. We have a complicated study design, and as far as I have been able to tell, there are no published statistical packages that can deal with this design correctly. We have a blocked design, of 3 blocks, with each 5 plots with each a different treatment. Each of these 15 plots has been sampled for plant, insect and bird species richness during 4 consecutive years. We would like to analyze all this in a mixed model where we include plot nested in block, and also the year effect as random factors. But this seems not to be possible, since the nested design has an "exchangeable correlation structure" (in GEE terms), or compound symmetry, whereas the time series is auto-regressive. Hence, we would like to construct a model that combines different correlation structures for the different random factors. My question to you is of course whether something like this is currently possible, if yes how? and if no, what would your advise be to analyze these data. Feel free to post this question on one of the GLMM-fora We hope you can give us some advice. On behalf of me and my colleagues`
Short answer: not that I know of (maybe AS-REML?) You will probably have to 'roll your own' with WinBUGS/JAGS, or AD Model Builder. I would also be quite concerned about fitting a model of this complexity to a data set of this size -- it's going to be hard to estimate a year effect with n=4, let alone an autoregressive correlation term. I would be inclined to fit a simpler model: year as a fixed effect -- and then test/examine the residuals for autocorrelation within plots. Hopefully others will come forward with different ideas. [cc'ing to r-sig-mixed-models] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBAgAGBQJSStv3AAoJEOCV5YRblxUHzhAIALS/9jKqgjuJHFmBG3uibMyB q+4W44WXR6tOSQYy0CSuLZHNdy+FfM2nXF7VDmyrwEZOfsx6s3S4jTEbxUauFxnG oUacy1ZsXJyp59FWN8m0LKTUutsYPebZRRZ9I3S6WXLRHSG3uv1iL8/qRlEvG2ZA oh/NK+1GP0UXgIYIdBgBwUmjc7hqCA4PGHxW7iDZ69dqpbZ306H8r2OuonzMvC8A uVzjiAHXF789njVAiNN154wCOLHIHn/6IfcHLx04wRLEBMqGMMIsBs3UfhDBMbZL NXIAq6ce5rvhpBWhQH8n94IwTTkc74WMmIZhaefkPbil97IzAEyeIgYYiP4DJV4= =N+gU -----END PGP SIGNATURE-----