[R-sig-eco] Changing the reference level of a factor

[Marcelino de la Cruz]

Hi Manuel,

You must assign the releveled factor to something. Try this

nidprop$treatment <- relevel(nidprop$treatment, ref="c")

modelo1 <- lm(hight ~ treatment, data = nidprop)

  summary(modelo1)


Cheers,

Marcelino


At 14:11 18/05/2010, Manuel Spínola wrote:
>Dear list members,
>
>I am trying to change the reference level of a 
>factor but when I run a model with the lm 
>function the new order it does not taking place 
>(I still have the old order of the levels).
>
> > relevel(nidprop$treatment, ref="c", data=nidprop)
>[1] a a a a b b b b c c c c
>Levels: c a b
>
> > modelo1 = lm(hight ~ treatment, data = nidprop)
>
> > summary(modelo1)
>
>Call:
>lm(formula = hight ~ treatment, data = nidprop)
>
>Residuals:
>    Min      1Q  Median      3Q     Max
>-1.6052 -1.0626 -0.0950  0.9228  3.0768
>
>Coefficients:
>               Estimate Std. Error t value Pr(>|t|)
>(Intercept)     37.9140     0.7368  51.461 1.98e-12 ***
>treatment[T.b]  -0.2298     1.0419  -0.221   0.8304
>treatment[T.c]  -3.1133     1.0419  -2.988   0.0153 *
>---
>Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
>
>Residual standard error: 1.474 on 9 degrees of freedom
>Multiple R-squared: 0.552,      Adjusted R-squared: 0.4525
>F-statistic: 5.545 on 2 and 9 DF,  p-value: 0.02696
>
>
>Any idea why?
>
>Best,
>
>Manuel Spínola
>
>--
>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
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>Fax: (506) 2237-7036
>
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________________________________

Marcelino de la Cruz Rot

Departamento de  Biología Vegetal
E.U.T.I. Agrícola
Universidad Politécnica de Madrid
28040-Madrid
Tel.: 91 336 54 35
Fax: 91 336 56 56
marcelino.delacruz at upm.es
_________________________________