Do I need random effects?

Thanks, David.

One or two glitches remain:

 > anova(m1, m0)
Data: Pastes
Models:
m1: strength ~ (1 | batch)
m0: strength ~ (1 | dummy)
    Df    AIC    BIC  logLik Chisq Chi Df Pr(>Chisq)
m1  3 308.60 314.88 -151.30
m0  3 316.26 322.55 -155.13     0      0          1
 > anova(m0,m1)
Data: Pastes
Models:
m0: strength ~ (1 | dummy)
m1: strength ~ (1 | batch)
    Df    AIC    BIC  logLik  Chisq Chi Df Pr(>Chisq)
m0  3 316.26 322.55 -155.13
m1  3 308.60 314.88 -151.30 7.6651      0  < 2.2e-16 ***
---
Signif. codes:  0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1

The df's are not what we want them to be - and I am rather surprised to 
find a p-value. :-)

Murray

dummy <- rep(1,nrow(Pastes))
m1 <- lmer(strength ~ (1|batch), Pastes, REML=F)
m0 <- lmer(strength ~ (1|dummy), Pastes, REML=F)
anova(m1, m0)

Dr Murray Jorgensen      http://www.stats.waikato.ac.nz/Staff/maj.html
Department of Statistics, University of Waikato, Hamilton, New Zealand
Email: maj at waikato.ac.nz    majorgensen at ihug.co.nz      Fax 7 838 4155
Phone  +64 7 838 4773 wk    Home +64 7 825 0441   Mobile 021 0200 8350