[EMAIL PROTECTED] writes: > Hi Community, > > I'm trying to reconcile Cook's Distances computed in glm. The > following snippet of code shows that the Cook's Distances contours on > the plot of Residuals v Leverage do not seem to be the same as the > values produced by cooks.distance() or in the Cook's Distance against > observation number plot. > > counts <- c(18,17,15,20,10,20,25,13,12) > outcome <- gl(3,1,9) > treatment <- gl(3,3) > d.AD <- data.frame(treatment, outcome, counts) > glm.D93 <- glm(counts ~ outcome + treatment, family=poisson()) > > opar <- par(mfrow=c(2,1)) > plot(glm.D93, which=c(4,5)) > par(opar) > > cooks.distance(glm.D93) > > The difference is reasonably moderate in this case. My suspicions > were aroused by a case in which the plot showed five or size points > greater than 1, none of which could be identified in the output of the > function.
Hmm, yes. A good guess is that the contour levels need to be modified by a dispersion factor. The plot is much more consistent with cooks.distance(glm.D93,dispersion=5.129/4 ) -- O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
