I'm puzzled by the behaviour of factors in rma models, see example and comments below. I'm sure there's a simple explanation but can't see it...
Thanks for any input John Hodgson ------------------------------------- code/selected output ----------------- library(metafor) ## Set up data (from Lenters et al A Meta-analysis of Asbestos and Lung Cancer... ## Environmental Health Perspectives • volume 119 | number 11 | November 2011) KL = c(0.02905, 0.06929, -0.1523, 1.6441, 0.1215, 0.3975, 1.0566, 0.1257, 0.2277, 0.06791, 0.08164, 0.2526, 0.07577, 0.03266, 0.1141, 0.1836, 1.8276, 0.4149, 15.4974) SE = c(0.006633, 0.09335, 0.08909, 0.4297, 0.07858, 0.1753, 0.3679, 0.1837, 0.2172, 0.2775, 0.4201, 0.1976, 0.7688, 0.06507, 0.06239, 0.09061, 0.9509, 0.2181, 7.331) VL = SE*SE amph = c(0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) mix = c(0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) ftype = c(0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2) factor(amph) factor(ftype) factor(mix) ## Fit ftype... > rma(KL,VL,mods=ftype) Mixed-Effects Model (k = 19; tau^2 estimator: REML) tau^2 (estimate of residual amount of heterogeneity): 0.0111 (SE = 0.0095) tau (sqrt of the estimate of residual heterogeneity): 0.1054 Test for Residual Heterogeneity: QE(df = 17) = 43.0937, p-val = 0.0005 Test of Moderators (coefficient(s) 2): QM(df = 1) = 1.1069, p-val = 0.2928 Model Results: estimate se zval pval ci.lb ci.ub intrcpt 0.0811 0.0606 1.3380 0.1809 -0.0377 0.2000 mods 0.0473 0.0449 1.0521 0.2928 -0.0408 0.1353 Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 ## why only one df for the 2-level factor? ## in other words, why isn't the above model the same as the following... > > > > rma(KL,VL,mods=cbind(amph,mix)) Mixed-Effects Model (k = 19; tau^2 estimator: REML) tau^2 (estimate of residual amount of heterogeneity): 0.0030 (SE = 0.0046) tau (sqrt of the estimate of residual heterogeneity): 0.0549 Test for Residual Heterogeneity: QE(df = 16) = 37.5762, p-val = 0.0017 Test of Moderators (coefficient(s) 2,3): QM(df = 2) = 6.9220, p-val = 0.0314 Model Results: estimate se zval pval ci.lb ci.ub intrcpt 0.0380 0.0402 0.9448 0.3447 -0.0408 0.1169 amph 0.2879 0.1163 2.4754 0.0133 0.0599 0.5158 * mix 0.0888 0.0625 1.4199 0.1556 -0.0338 0.2114 --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 > -- View this message in context: http://r.789695.n4.nabble.com/Factor-moderators-in-metafor-tp4639745.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.