Dear all, I wish to thank Christoph Buser and John Wilkinson for their input, and especially John his examples and for for pointing me to the thread 'Doubt about nested aov output' where the rat-example was hiding...: http://search.gmane.org/?query=Doubt+about+nested+aov+output&email=&group=gmane.comp.lang.r.general&sort=revdate&DEFAULTOP=and&xP=doubt.nested.aov.output.&xFILTERS=Gcomp.lang.r.general---A In this great thread you find a description not only on using aov on this nested rat-data, but also how to handle it with lmer, e.g. model specification and coding of grouping levels. Best regards, Henrik -- ************************ Henrik P?rn Department of Biology NTNU 7491 Trondheim Norway +47 735 96282 (office) +47 909 89 255 (mobile) +47 735 96100 (fax)