[R] is this an ANOVA ?
ubuntu.diego at gmail.com
Wed Apr 13 02:10:26 CEST 2011
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
I wrote a linear model for this:
This is the output:
lm(formula = y ~ x, data = MD)
Min 1Q Median 3Q Max
-2.000e+00 -1.000e+00 5.551e-17 1.000e+00 2.000e+00
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 ?
2) Is there a (easy) way to plot, mean plus/minus 2*sd for each substrate type ? (with asterisks denoting significant differences ?)
system x86_64, darwin9.8.0
svn rev 52157
version.string R version 2.11.1 (2010-05-31)
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