lme4: Error in getResponseFormula(form) : "Form" must be a two sided formula
I'm sure I'm being stupid so flame away... R2.2.1 on Windoze (boohoo) latest updates of packages. I'm exploring a dataset (land) with three variables looking at an narrowly unbalanced two group (GROUP) ANCOVA of a randomised controlled trial analysing endpoint score (SFQ.LOCF.ENDPOINT) entering the baseline score (SFQ.BASELINE) as covariate and the following work fine:
res.same <- lm(SFQ.LOCF.ENDPOINT ~ SFQ.BASELINE + GROUP,land) res.diff <- lm(SFQ.LOCF.ENDPOINT ~ SFQ.BASELINE + GROUP + SFQ.BASELINE*GROUP,land) anova(res.same,res.diff)
I try:
lmList(SFQ.LOCF.ENDPOINT ~ SFQ.BASELINE | GROUP, land)
Call: Error in getResponseFormula(form) : "Form" must be a two sided formula I'm puzzled. That looks like a two sided formula very like the one in the help for lme4 (which had been loaded) and the data look OK:
table(land$SFQ.LOCF.ENDPOINT)
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 23 1 1 2 4 8 5 16 9 7 14 18 7 16 9 6 8 4 6 2 3
table(land$SFQ.BASELINE)
3 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 1 1 3 3 4 11 7 7 10 12 9 16 14 9 8 7 8 6 1 1
table(land$GROUP)
1 2 87 89 Advice accepted gratefully and flames ruefully! Chris
Chris Evans <chris at psyctc.org> Consultant Psychiatrist in Psychotherapy, Rampton Hospital; Research Programmes Director, Nottinghamshire NHS Trust, Hon. Professor of Psychotherapy, Nottingham University, Hon. SL Institute of Psychiatry *** My views are my own and not representative of those institutions ***