Re: [R] factorial anova

From: John Sorkin <jsorkin_at_grecc.umaryland.edu>
Date: Mon 26 Dec 2005 - 15:40:49 EST


Rick,
I read you data into a data.frame called data.

I sugguest you run the model as follows: fit<-anova( dosel ~ estado * Bosque, data = data) summary(fit1)

The results are:

> contrasts(data$Bosque)

         siemprev
deciduo         0
siemprev        1


> contrasts(data$estado)
pristino activo 0 pristino 1

> summary(fit1)

Call:
lm(formula = dosel ~ estado * Bosque, data = data)

Residuals:

    Min 1Q Median 3Q Max -30.160 -2.548 0.312 3.588 21.840

Coefficients:

                               Estimate Std. Error  t value Pr(>|t|)    
(Intercept)                   5.632e+01  5.769e+00    9.762 3.84e-08 ***
estadopristino                3.453e+01  8.159e+00    4.232 0.000635 ***
Bosquesiemprev                1.249e-15  8.159e+00 1.53e-16 1.000000    
estadopristino:Bosquesiemprev 5.408e+00 1.154e+01 0.469 0.645622
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 

Residual standard error: 12.9 on 16 degrees of freedom
Multiple R-Squared: 0.7245,     Adjusted R-squared: 0.6729 
F-statistic: 14.03 on 3 and 16 DF,  p-value: 9.615e-05 

You will note that the p values for the interaction and the main effect for Bosqueiemprev are no longer the same.


Feliz ano nuevo!

John


John Sorkin M.D., Ph.D.
Chief, Biostatistics and Informatics
Baltimore VA Medical Center GRECC and
University of Maryland School of Medicine Claude Pepper OAIC

University of Maryland School of Medicine
Division of Gerontology
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524

410-605-7119 
- NOTE NEW EMAIL ADDRESS:
jsorkin@grecc.umaryland.edu
>>> Rick Bilonick <rab@nauticom.net> 12/25/05 9:09 PM >>>
On Sun, 2005-12-25 at 23:01 -0300, Petra Wallem wrote:

> Hello every body, I am trying to do a factorial anova analysis
> following this model:
>
> model<-anova(lm(responsevariable~factorA*factorB))
> model<-anova(lm(luz$dosel~luz$estado*luz$Bosque))
>
> Df Sum Sq Mean Sq F value Pr(>F)
> estado 1 6931.1 6931.1 41.6455 7.974e-06 ***
> Bosque 1 36.6 36.6 0.2197 0.6456
> estado:Bosque 1 36.6 36.6 0.2197 0.6456
> Residuals 16 2662.9 166.4
>
> Strange is that the sum of squares of the factor Bosque are identical to
> the SS of the interaction, and are non significant. But when I plot the
> data, the interaction surley is significant...
>
> my data.frame looks as follows:
>
> Bosque estado lux dosel
> 1 deciduo pristino 703 88.56
> 2 deciduo pristino 800 90.64
> 3 deciduo pristino 150 95.84
> 4 deciduo pristino 245 87.52
> 5 deciduo pristino 1300 91.68
> 6 deciduo activo 1900 26.16
> 7 deciduo activo 840 59.44
> 8 deciduo activo 323 69.84
> 9 deciduo activo 112 75.04
> 10 deciduo activo 1360 51.12
> 11 siemprev activo 900 41.76
> 12 siemprev activo 480 65.68
> 13 siemprev activo 350 78.16
> 14 siemprev activo 350 37.60
> 15 siemprev activo 272 58.40
> 16 siemprev pristino 100 94.80
> 17 siemprev pristino 60 95.84
> 18 siemprev pristino 50 97.92
> 19 siemprev pristino 270 94.80
> 20 siemprev pristino 110 97.92
>
> Dose some body understand what I am doing wrong??? I have been
> navigating at the R site search, but didn't found much posting on
> factorial anova.
>
> In advance thanks a lot for your comments
> Petra
>
> ______________________________________________
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> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
It would help if you would use the "dump" function and paste the output into an e-mail:
> dump("luz","")
Also, it's much easier to use "data=luz" as an argument in the lm function rather than appending the data frame name to each variable. I don't think that "model" contains the lm model output. It looks like you are saving the anova table. ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Received on Mon Dec 26 15:48:51 2005

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