Hello;

When I run an anova to compare two lmer models I have in some situations
(always when I compare a model with interactions with a model where I
removed one simple fixed effect) an output that I don't fully understand. In
the anova output the models have the same degrees of freedom, as well as AIC
and BIC; the Chisq and its degrees of freedom are 0, and the p value is 1.
This makes me think that I cannot make this model comparison, but I would
like to understand why and to know how could I correctly compare two models
of this type.
The R output is below, any help or suggestions would be greatly appreciated!

Catarina

R version 2.13.0 (2011-04-13)

>
m2_Exp<-lmer(lat_perch~(Sex+Origin+trial)^2+SMI_Neo+(1|Nest_ID)+(1|ID),data=full,REML=F)

# lat_perch and SMI are numeric, but the other variables are factors

>
m2_Exp_Origin<-lmer(lat_perch~(Sex+Origin+trial)^2+SMI_Neo-Origin+(1|Nest_ID)+(1|ID),data=full,REML=F)

> anova(m2_Exp,m2_Exp_Origin)  # NS but sething wierd is happening
Data: full
Models:
m2_Exp: lat_perch ~ (Sex + Origin + trial)^2 + SMI_Neo + (1 | Nest_ID) +
m2_Exp:     (1 | ID)
m2_Exp_Origin: lat_perch ~ (Sex + Origin + trial)^2 + SMI_Neo - Origin + (1
|
m2_Exp_Origin:     Nest_ID) + (1 | ID)
              Df  AIC    BIC logLik Chisq Chi Df Pr(>Chisq)
m2_Exp        14 3056 3098.9  -1514
m2_Exp_Origin 14 3056 3098.9  -1514     0      0          1

> summary(m2_Exp)
Linear mixed model fit by maximum likelihood
Formula: lat_perch ~ (Sex + Origin + trial)^2 + SMI_Neo + (1 | Nest_ID)
+      (1 | ID)
   Data: full
  AIC  BIC logLik deviance REMLdev
 3056 3099  -1514     3028    2865
Random effects:
 Groups   Name        Variance Std.Dev.
 ID       (Intercept) 2516808  1586.45
 Nest_ID  (Intercept)  481927   694.21
 Residual             9961255  3156.15
Number of obs: 158, groups: ID, 53; Nest_ID, 18

Fixed effects:
                    Estimate Std. Error t value
(Intercept)         -3995.97    3731.88  -1.071
SexMale             -1754.35    1225.74  -1.431
OriginUrban          1618.35    1268.25   1.276
trialT2             -2989.72    1128.92  -2.648
trialT3             -1457.01    1145.84  -1.272
SMI_Neo                98.49      43.34   2.272
SexMale:OriginUrban    64.10    1390.64   0.046
SexMale:trialT2      1364.19    1230.84   1.108
SexMale:trialT3      2570.80    1237.91   2.077
OriginUrban:trialT2  -336.72    1231.60  -0.273
OriginUrban:trialT3   821.13    1238.67   0.663

Correlation of Fixed Effects:
            (Intr) SexMal OrgnUr trilT2 trilT3 SMI_Ne SxM:OU SxM:T2 SxM:T3
OrU:T2
SexMale
-0.066
OriginUrban -0.127
0.380
trialT2     -0.106  0.312
0.299
trialT3      0.009  0.324  0.304
0.499
SMI_Neo     -0.962 -0.120 -0.063 -0.047
-0.165
SxMl:OrgnUr -0.047 -0.593 -0.578 -0.007 -0.030
0.159
SexMl:trlT2  0.118 -0.498 -0.027 -0.609 -0.296 -0.027
-0.004
SexMl:trlT3  0.077 -0.505 -0.033 -0.304 -0.607  0.016  0.009
0.496
OrgnUrbn:T2  0.135 -0.025 -0.482 -0.608 -0.293 -0.044 -0.007  0.061
0.029
OrgnUrbn:T3  0.130 -0.029 -0.483 -0.301 -0.598 -0.039  0.001  0.031  0.070
0.498

	[[alternative HTML version deleted]]


