[R-sig-ME] Linear mixed effect model

[Ben Bolker]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 11-03-19 11:27 AM, Manuel Spínola wrote:
> Thank you very much Ben,
> 
> I decided to keep "otter" as a random factor:
> 
> modA = lmer(Swiftness.1 ~ Lure + Sex + Facility.Size + (1|Subject), REML
> = F, data = otter)
> summary(modA)
> 
> modB = lmer(Swiftness.1 ~ (1|Subject), REML = F, data = otter)
> summary(modB)
> 
> modC = lmer(Swiftness.1 ~ Lure + (1|Subject), REML = F, data = otter)
> summary(modC)
> 
>> AICctab(modA, modB, modC, weights = T, delta = TRUE, base = T, sort =
> TRUE, nobs = 17)
>      AICc   df dAICc  weight
> modB 1313.1 3     0.0 1    
> modC 1336.3 8    23.2 <0.001
> modA 1374.5 11   61.4 <0.001
> 
> Output for best model:
> 
>> summary(modB)
> Linear mixed model fit by maximum likelihood
> Formula: Swiftness.1 ~ (1 | Subject)
>    Data: otter
>   AIC  BIC logLik deviance REMLdev
>  1311 1319 -652.6     1305    1298
> Random effects:
>  Groups   Name        Variance Std.Dev.
>  Subject  (Intercept)     0      0.00 
>  Residual             21133    145.37 
> Number of obs: 102, groups: Subject, 17
> 
> Fixed effects:
>             Estimate Std. Error t value
> (Intercept)    99.76      14.39   6.931
> 
> 
> Is it fair to say that there is no effect of any of the factors?
> Did you say that the variance 0 in the random effect output is low power?
> 

  Yes, although technically I would say that the factors are not useful
for prediction; if you want to test for the presence of a significant
effect, then fit the full model and report the p-values and confidence
intervals from it.  Yes, I would say that the zero variance represents
noise/ low power: if you were to do the equivalent aov()-analysis it
would probably report a negative variance (i.e., among-group mean square
< within-group mean square).

  Ben
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.10 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

iEYEARECAAYFAk2E0bYACgkQc5UpGjwzenNYEgCfVyZWOsGQKku23cl9P2QYJE2P
xf4AmQESmtzRM01AIdBJ38clLc9c2JXA
=OGDG
-----END PGP SIGNATURE-----