
Dear R users,

I am trying to fit the following ANCOVA model in R2.4.0

Y_ij=mu+alpha_i+beta*(X_ij-X..)+epsilon_ij

Particularly I am interested in obtaining estimates for mu, and the effects 
alpha_i


I have this data (from the book Applied Linear Statistical Models by Neter 
et al (1996), page 1020)


y<-c(38,43,24,39,38,32,36,38,31,45,27,21,33,34,28)
x<-c(21,34,23,26,26,29,22,29,30,28,18,16,19,25,29)
xmean<-x-mean(x)
grupo<-factor(rep(c(1,2,3),5))
datos<-data.frame(y,xmean,grupo)

and I have done the following

modelo<-lm(y~xmean+grupo,data=datos)

summary(modelo)

Call:
lm(formula = y ~ xmean + grupo, data = datos)

Residuals:
     Min      1Q  Median      3Q     Max
-2.4348 -1.2739 -0.3363  1.6710  2.4869

Coefficients:
             Estimate Std. Error t value Pr(>|t|)
(Intercept)  39.8174     0.8576  46.432 5.66e-14 ***
xmean         0.8986     0.1026   8.759 2.73e-06 ***
grupo2       -5.0754     1.2290  -4.130  0.00167 **
grupo3      -12.9768     1.2056 -10.764 3.53e-07 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 1.873 on 11 degrees of freedom
Multiple R-Squared: 0.9403,     Adjusted R-squared: 0.9241
F-statistic: 57.78 on 3 and 11 DF,  p-value: 5.082e-07


In the book, the estimates are

 From this book,

mu=33.8
alpha_1=6.017
alpha_2=0.942
beta=0.899

Is it possible to obtain this estimates and their standard errors from the 
model I fitted?

Thanks in advance

Tomas Goicoa

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