[R] treatment contrasts and summary.lm

[Berton Gunter]

?C  ?contr.treatment  may help. Also 6.2 of Venables's and Ripley's MASS for
a more thorough discussion.

The coefficients are the differences between the mean at the stated levels
of the factor and the first level.

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box
 
 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of 
> Christoph Scherber
> Sent: Thursday, December 02, 2004 3:01 AM
> To: R-help at stat.math.ethz.ch
> Subject: [R] treatment contrasts and summary.lm
> 
> Dear list members,
> 
> I have a 2-factor ANOVA where the summary.lm output looks like this 
> (using treatment contrasts):
> 
>                     Value Std. Error t value Pr(>|t|)
>       (Intercept)  0.0389  0.0220     1.7695  0.0817
> as.factor(Block)1  0.0156  0.0066     2.3597  0.0215
> as.factor(Block)2 -0.0018  0.0037    -0.4857  0.6289
> as.factor(Block)3 -0.0007  0.0026    -0.2812  0.7795
>    as.factor(AZ)1 -0.0066  0.0076    -0.8670  0.3893
>    as.factor(AZ)2  0.0064  0.0047     1.3530  0.1810
>    as.factor(AZ)3 -0.0015  0.0031    -0.4863  0.6284
>    as.factor(AZ)4  0.0054  0.0025     2.1499  0.0355
>    as.factor(AZ)5  0.0062  0.0037     1.6653  0.1009
> 
> Block has 4 levels and AZ has 6 levels. My question now is: 
> What exactly 
> do the values for AZ show? I know it´s somehow differences between 
> intercepts, but it would be great if someone could tell me 
> more on how 
> exactly to interprete the output.
> 
> Thanks very much in advance!
> Christoph
> 
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