I am running a Poisson regression with a single outcome variable, HGE, and a single independent variable, a factor, Group which can be one of two values, Group1, or Group2. I am trying to define contrasts that will give me the values of my outcome variable (HGE) when group=Group1 and when group=Group2. After beating my head against a wall day, I have decided to ask for help.
Please see code and below below. DataForR <- structure(list(Group = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L), .Label = c("Group1", "Group2"), class = "factor"), HGE = c(3, 1, 0, 0, 0, 1, 0, 0, 0, 0, 3, 5, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 3, 2, 0, 0, 0, 0, 3, 0, 2, 3, 0, 2, 0, 0, 5, 0, 0, 0, 1, 0, 1, 3, 3, 4, 1, 0, 0, 2, 0, 0, 6, 2, 0, 0, 1, 4, 5, 0, 3, 11, 0, 0, 0, 2), logFU = c(3.11397816503905, 2.68510374827232, 0.991192040047273, 0.611801541105993, 1.06925022633126, 2.57001131045749, 0.527354925717201, 0.608027951722353, 1.35812348415319, 1.99809590222588, 2.73814823225949, 2.89037175789616, 1.02290046693241, 0.58120642052779, 1.03160157838515, 0.457336938815005, 1.56760267327335, 2.29561642367795, -0.296984465114094, 0.4812251539897, 0.606135803570315, -0.349754501094159, 1.34464013381591, 1.03777062941186, 0.604240068405416, 0.416972714959644, 1.90748277192143, 1.92586939817187, 2.84013378690079, 0.611801541105993, 1.57697211118452, 1.09047743846183, 0.412385550952738, -0.129570991408426, 0.752136479035649, 1.3518538711396, 1.44118361285158, 1.24779030782599, 1.0893098960058, 1.40008768325223, 1.36257783450257, 1.06686359035353, 1.93493747038584, 0.549645615615573, -0.0794641713542468, -0.220542769614152, 2.18753270073519, 0.613683009205699, 1.74010061095415, 1.76596671466633, 0.508740117274969, 1.71791855542817, 1.90335053463652, 1.24679280150886, 0.541597282432744, 2.16984703638892, 1.91926871414052, 1.030363188134, 1.07992015565596, 1.78886175639198, 1.07755887947028, -0.117783035656384, 1.49866152280324, 1.03530757397947, 2.68225744654048, 1.58909347171687, 1.49477500411396, 1.47749256296521, 1.77129690199719, 1.5668782980153, 2.06633519417454, 2.62758302063679)), class = "data.frame", row.names = c(NA, -72L)) # Show that dataForR is a dataframe. summary(dataForR) levels(dataForR$Group) class(dataForR$Group) # Fit the model. fit0 <- glm(HGE ~ Group,family=poisson,data=dataForR,offset=logFU) summary(fit0) # Get value for Group1 MyContrast=list(xxx=c(1,0)) MyContrast contrast(fit0,MyContrast) # Get value for Group2 MyContrast=list(xxx=c(1,1)) MyContrast contrast(fit0,MyContrast) I hope you can help me understand how to use the contrast statement. Thank you, John John David Sorkin M.D., Ph.D. Professor of Medicine Chief, Biostatistics and Informatics University of Maryland School of Medicine Division of Gerontology and Geriatric Medicine Baltimore VA Medical Center 10 North Greene Street GRECC (BT/18/GR) Baltimore, MD 21201-1524 (Phone) 410-605-7119 (Fax) 410-605-7913 (Please call phone number above prior to faxing) [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.