Achaz von Hardenberg
2009-Nov-26 16:17 UTC
[R] different fits for geese and geeglm in geepack?
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It looks strange. If you send me data for a small reproducible example then I'll look into the issue. Regards S?ren ________________________________________ Fra: r-help-bounces at r-project.org [r-help-bounces at r-project.org] På vegne af Achaz von Hardenberg [achaz.hardenberg at gmail.com] Sendt: 26. november 2009 17:17 Til: r-help at r-project.org Emne: [R] different fits for geese and geeglm in geepack? Dear all, I am trying to fit a GEE model on eagle productivity (number of hatched offspring per nest) using the geeglm function in the library geepack and I found an odd result. My understanding is that the function geese and geeglm should give the same fits, as actually geeglm uses geese to fit the model, providing a glm style output. However, if I fit the same model with geeglm and geese I get slightly different estimates of the parameters. Most striking is the difference between the estimates of the correlation parameter where the differences are huge: (geese: alpha= -0.0727, se= 0.0608; geeglm: -0.219, se= 0.091). Anybody knows why this is like that and which of the two I should rather trust? (I attach the outputs of the two models at the end of this mail) thanks a lot for your hints! Achaz von Hardenberg PS: One more question actually: anybody has got some code to calculate the QICu values to compare GEE models with and without specific fixed factors using geepack? ################## GEESE OUTPUT: Call: geese(formula = PROD ~ as.factor(clas3) + Twinter + Tprecova, id = Nterr, waves = anno, data = aquile.dat2, family = poisson, corstr = "ar1") Mean Model: Mean Link: log Variance to Mean Relation: poisson Coefficients: estimate san.se wald p (Intercept) -1.7850 0.3661 23.77 1.08e-06 as.factor(clas3)2 0.7165 0.2475 8.38 3.79e-03 as.factor(clas3)3 0.5052 0.3368 2.25 1.34e-01 Twinter -0.1066 0.0464 5.28 2.16e-02 Tprecova -0.0549 0.0368 2.22 1.36e-01 Scale Model: Scale Link: identity Estimated Scale Parameters: estimate san.se wald p (Intercept) 0.764 0.123 38.6 5.17e-10 Correlation Model: Correlation Structure: ar1 Correlation Link: identity Estimated Correlation Parameters: estimate san.se wald p alpha -0.0727 0.0608 1.43 0.232 Returned Error Value: 0 Number of clusters: 21 Maximum cluster size: 20 ############################################### GEEGLM OUTPUT: Call: geeglm(formula = PROD ~ as.factor(clas3) + Twinter + Tprecova, family = poisson, data = aquile.dat2, id = Nterr, waves = anno, corstr = "ar1") Coefficients: Estimate Std.err Wald Pr(>|W|) (Intercept) -1.7992 0.3751 23.01 1.6e-06 *** as.factor(clas3)2 0.7412 0.2623 7.99 0.0047 ** as.factor(clas3)3 0.5253 0.3335 2.48 0.1152 Twinter -0.1083 0.0473 5.24 0.0220 * Tprecova -0.0483 0.0354 1.86 0.1721 --- Signif. codes: 0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1 Estimated Scale Parameters: Estimate Std.err (Intercept) 0.773 0.117 Correlation: Structure = ar1 Link = identity Estimated Correlation Parameters: Estimate Std.err alpha -0.219 0.091 Number of clusters: 21 Maximum cluster size: 20 Dr. Achaz von Hardenberg -------------------------------------------------------------------------------------------------------- Centro Studi Fauna Alpina - Alpine Wildlife Research Centre Servizio Sanitario e della Ricerca Scientifica Parco Nazionale Gran Paradiso, Degioz, 11, 11010-Valsavarenche (Ao), Italy Present address: National Centre for Statistical Ecology School of Mathematics, Statistics and Actuarial Science, University of Kent, Canterbury, UK E-mail: achaz.hardenberg at pngp.it fauna at pngp.it Skype: achazhardenberg Mobile: +44.(0)783.266.5995 Dr. Achaz von Hardenberg -------------------------------------------------------------------------------------------------------- Centro Studi Fauna Alpina - Alpine Wildlife Research Centre Servizio Sanitario e della Ricerca Scientifica Parco Nazionale Gran Paradiso, Degioz, 11, 11010-Valsavarenche (Ao), Italy Present address: National Centre for Statistical Ecology School of Mathematics, Statistics and Actuarial Science, University of Kent, Canterbury, UK E-mail: achaz.hardenberg at pngp.it fauna at pngp.it Skype: achazhardenberg Mobile: +44.(0)783.266.5995 -------------------------------------------------------------------------------------------------------- [[alternative HTML version deleted]]