is this an ANOVA ?

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Ubuntu Diego
Sent: April-12-11 5:10 PM
To: r-help at r-project.org
Subject: [R] is this an ANOVA ?

Hi all,
	I have a very easy questions (I hope). I had measure a property of plants, growing in three
different substrates (A, B and C). The rest of the conditions remained constant. There was very high
variation on the results.
	I want to do address, whether there is any difference in the response (my measurement) from
substrate to substrate?

x<-c('A','A','A','A','A','B','B','B','B','B','C','C','C','C','C') # Substrate type
y <- c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15) # Results of the measurement
MD<-data.frame(x,y)

	I wrote a linear model for this:

summary(lm(y~x,data=MD))

	This is the output:

Call:
lm(formula = y ~ x, data = MD)

Residuals:
       Min         1Q     Median         3Q        Max
-2.000e+00 -1.000e+00  5.551e-17  1.000e+00  2.000e+00

Coefficients:
            Estimate Std. Error t value Pr(>|t|)
(Intercept)   3.0000     0.7071   4.243 0.001142 **
xB            5.0000     1.0000   5.000 0.000309 ***
xC           10.0000     1.0000  10.000 3.58e-07 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 1.581 on 12 degrees of freedom
Multiple R-squared: 0.8929,	Adjusted R-squared: 0.875
F-statistic:    50 on 2 and 12 DF,  p-value: 1.513e-06

	I conclude that there is an effect of substrate type (x).
	NOW the questions :
		1) Do the fact that the all p-values are significant means that all the groups are
different from each other ?