Yes, in essence although it is much easier to describe in words. anova uses the Chisquared-based estimate of dispersion unless it is known. drop1 uses the deviance-based estimate of dispersion unless it is known.
If the F tests are going to be approximately valid the dispersion estimators should be pretty similar, and when they are not the first _may_ be closer to chi-square-distributed. However, as I recall it, when I learnt analysis of deviance using GLIM3, the drop1 approach was used. On Thu, 20 Oct 2005, Tom Van Dooren wrote: > Hi Brian, > well I wanted a test based on quasibinomial... > Does it work like this then?: > > x<-gl(3,2) > y<-c(0,1,0,0,1,1) > > # quasibinomial models # > ######################## > > qb1<-glm(y~x,quasibinomial) > qb2<-glm(y~1,quasibinomial) > > qbdev<-(qb2$dev-qb1$dev) > > qbdev # deviance I > > qbdev/(qb2$df.res-qb1$df.res)/(qb1$dev /qb1$df.res) # deviance ratio II > > qbdev/summary(qb1)$disp # scaled deviance III > > qbdev/(qb2$df.res-qb1$df.res)/summary(qb1)$disp # scaled deviance IV > > > anova(qb2,qb1,test="Chisq") # Chisq test based on I > drop1(qb1,test="F") # F test, based on II > drop1(qb1,test="Chisq") # Chisq test, based on III > anova(qb2,qb1,test="F") # F test, based on IV > > # binomial models # > ################### > > b1<-glm(y~x,binomial) > b2<-glm(y~1,binomial) > > bdev<-(b2$dev-b1$dev) > > bdev # deviance I > > bdev/(b2$df.res-b1$df.res)/(b1$dev /b1$df.res) # deviance ratio II > > > drop1(b1,test="Chisq") # Chisq test, based on I > anova(b2,b1,test="Chisq") # Chisq test based on I > anova(b2,b1,test="F") # Chisq test, based on I > drop1(b1,test="F") # F test, based on II > > > Cheers, Tom > > PS: thanks Tord ;) > > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html