[R] Using anova(f1, f2) to compare lmer models yields seemingly erroneous Chisq = 0, p = 1

[Alain Zuur]

rapton wrote:
> 
> Hello,
> 
> I am using R to analyze a large multilevel data set, using
> lmer() to model my data, and using anova() to compare the fit of various
> models.  When I run two models, the output of each model is generated
> correctly as far as I can tell (e.g. summary(f1) and summary(f2) for the
> multilevel model output look perfectly reasonable), and in this case (see
> below) predictor.1 explains vastly more variance in outcome than
> predictor.2
> (R2 = 15% vs. 5% in OLS regression, with very large N).  What I am utterly
> puzzled by is that when I run an anova comparing the two multilevel model
> fits, the Chisq comes back as 0, with p = 1.  I am pretty sure that fit #1
> (f1) is a much better predictor of the outcome than f2, which is reflected
> in the AIC, BIC , and logLik values.  Why might anova be giving me this
> curious output?  How can I fix it?  I am sure I am making a dumb error
> somewhere, but I cannot figure out what it is.  Any help or suggestions
> would 
> be greatly appreciated!
> 
> -Matt
> 
> 
>> f1 <- (lmer(outcome ~ predictor.1 + (1 | person), data=i))
>> f2 <- (lmer(outcome ~ predictor.2 + (1 | person), data=i))
>> anova(f1, f2)
> 
> Data: i
> Models:
> f1: outcome ~ predictor.1 + (1 | person)
> f2: outcome ~ predictor.2 + (1 | person)
>    Df    AIC      BIC    logLik   Chisq Chi Df Pr(>Chisq)
> f1  6  45443  45489 -22715
> f2 25  47317  47511 -23633     0     19          1
> 


** NOT  ** nested       ....sorry....the brain is going faster than the
fingers.





-----
--------------------------------------------------------------------
Dr. Alain F. Zuur
First author of:

1. Analysing Ecological Data (2007).
Zuur, AF, Ieno, EN and Smith, GM. Springer. 680 p.

2. Mixed effects models and extensions in ecology with R. (2009).
Zuur, AF, Ieno, EN, Walker, N, Saveliev, AA, and Smith, GM. Springer.

3. A Beginner's Guide to R (2009).
Zuur, AF, Ieno, EN, Meesters, EHWG. Springer


Statistical consultancy, courses, data analysis and software
Highland Statistics Ltd.
6 Laverock road
UK - AB41 6FN Newburgh
Email: highstat at highstat.com
URL: www.highstat.com



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