[R-sig-eco] CI for mixed models with lme

Manuel Spínola mspinola10 at gmail.com
Sat Sep 25 22:12:20 CEST 2010


  Dear list members,

I am fitting 2 linear mixed model with function lme and I cannot get the 
CI for "modelo2" with function "intervlas" (below are the output from 
the 2 models).
Any clue why?  Thank you very much in advance.  Manuel.

 > intervals(modelo1)$fixed
                 lower      est.     upper
(Intercept)  29.21725  42.85153  56.48581
tempo       -24.41173 -19.74592 -15.08011
attr(,"label")
[1] "Fixed effects:"

 > intervals(modelo2)$fixed
Error en intervals.lme(modelo2) :
   Cannot get confidence intervals on var-cov components: Non-positive 
definite approximate variance-covariance


modelo1 = lme(ipa ~ tempo, data=ipa, random = ~1 | localidad)
 > summary(modelo1)
Linear mixed-effects model fit by REML
  Data: ipa
        AIC      BIC    logLik
   2062.101 2075.172 -1027.050

Random effects:
  Formula: ~1 | localidad
         (Intercept) Residual
StdDev:    44.61678 36.95279

Fixed effects: ipa ~ tempo
                 Value Std.Error  DF   t-value p-value
(Intercept)  42.85153  6.898734 146  6.211507       0
tempo       -19.74592  2.360827 146 -8.363982       0
  Correlation:
       (Intr)
tempo 0

Standardized Within-Group Residuals:
         Min          Q1         Med          Q3         Max
-2.50376489 -0.45760686 -0.07812592  0.39097892  5.25554463

Number of Observations: 196
Number of Groups: 49


modelo2 = lme(ipa ~ tempo, random = ~1 | tempo/localidad, data=ipa)
 > summary(modelo2)
Linear mixed-effects model fit by REML
  Data: ipa
        AIC     BIC    logLik
   2144.981 2161.32 -1067.490

Random effects:
  Formula: ~1 | tempo
         (Intercept)
StdDev:    5.540235

  Formula: ~1 | localidad %in% tempo
         (Intercept) Residual
StdDev:     54.1832 19.60406

Fixed effects: ipa ~ tempo
                 Value Std.Error  DF   t-value p-value
(Intercept)  42.85153  4.961152 192  8.637415   0.000
tempo       -19.74592  4.437389   2 -4.449895   0.047
  Correlation:
       (Intr)
tempo 0

Standardized Within-Group Residuals:
         Min          Q1         Med          Q3         Max
-0.42528137 -0.17487600 -0.08655534  0.06944999  2.05895746

Number of Observations: 196
Number of Groups:
                tempo localidad %in% tempo
                    4                  196

-- 
Manuel Spínola, Ph.D.
Instituto Internacional en Conservación y Manejo de Vida Silvestre
Universidad Nacional
Apartado 1350-3000
Heredia
COSTA RICA
mspinola at una.ac.cr
mspinola10 at gmail.com
Teléfono: (506) 2277-3598
Fax: (506) 2237-7036



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