[R-sig-ME] Dealing with heteroscedasticity in repeated measure models

[Manuel Spínola]

  Dear list members,

I am fitting a repeated measure model using lme.
I have 4 measurements of a rate (variable called ipa) measured each year 
(variable called tempo, which was centered) on 48 counties (all the 
counties from a province, variable called localidad).
I am considering county like a random factor.
My models are:

model1 = lme(ipa ~ tempo, data=ipa, random = ~1 | localidad) # random 
intercept

model2 = lme(ipa ~ tempo, random = ~1 | tempo/localidad, data=ipa) # 
random intercept and slope

model3 = lme(ipa ~ tempo, random = ~1 | localidad, data=ipa, 
correlation=corAR1(form=~ tempo))

I have heteroscedasticity.
Is my last model dealing with heteroscedasticity?
Thank you very much in advance.
Best,

Manuel

-- 
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