aov and Error function
On 01/02/15 02:17, John Sorkin wrote:
I am trying to understand the Error function and its use in ANOVA. In particular I want to understand the difference between two models that differ only with respect to the Error statement: aovsubj <- aov(value~group+time+Error(subject),data=dataRMANOVA) and aovsubjgroup <- aov(value~group+time+Error(subject/group),data=dataRMANOVA) You will note that in my data I have two subject identifiers, subject and subject2. I am also trying to trying to understand how I should identify subjects, within group (i.e. intervention vs. control) or within time (0=baseline, 1=post)
Since no-one else seems to have answered you let me point out that your first formulation treats subject 1 in the "int" group as being the same as subject 1 in the "cont" group, and similarly for subject 2 and so on. The second formulation (subject nested within group) treats subject 1 in the "int" group as being *different* from subject 1 in the "cont" group. If you were using subject2 instead of subject there would (I *think*) be no difference between the two formulations. HTH cheers, Rolf Turner
Rolf Turner Technical Editor ANZJS Department of Statistics University of Auckland Phone: +64-9-373-7599 ext. 88276 Home phone: +64-9-480-4619