[R] Help Non-sequential ANOVAs

Ariane Charaoui
Thu, 28 Jul 2011 18:37:58 -0000

Hello,

I have data
on the maturity of two morphs of fish. I want to test whether their maturity is
evolving differently or not on a temporal scale (month). The maturity variable
(independent
variable) is continuous and the morph and month variables (dependant variables)
are categorical. Because the data show variance heterogeneity, I modeled it
with the function gls:

kg1 gls(maturity~morph*month, weights = varIdent(form = ~ 1 |morph*month) ,
na.action=na.omit, method="ML")

Next, I
want to test if the two effects “morph” and “month” are significant so I use
the function anova

anova(kg1)

Denom. DF: 75

                                   numDF            F-value          p-value

(Intercept)                   1
                     174.20833       <.0001

morph                         1
                   5.37109           0.0232

month                         5                      46.41181
         <.0001

morph:month              5                       2.85388
        0.0206



The problem is that I
want the results of a non-sequential anova. I tried also the function Anova,
but I get an error message:



Error in !factors[,
term2] : invalid argument type



Is there a way to fix
this problem or is it possible to specify a non-sequential anova?



Thank you



Ariane





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