[R] anova with ordered groups

From: Michele Pinelli <michele.pinelli_at_unina.it>
Date: Wed, 12 Nov 2008 16:18:54 +0100


Hi,
I have to do a comparison among three groups of genetic transcription levels.

I have a situation like this:

group 0: baseline
group 1: first treatment
group 2: second treatment

In the first group, I have only 2 samples, in the second one 4 samples and in the last group I have 10 samples.

I would check if the trnascription of a gene increases from the baseline situation to the fist treatment AND from the first treatment to the second treatment.

I did a table like this:
GENE-LEVEL, GROUP

10,0
12,0
22,1
23,1
21,1
24,1
31,2
32,2
33,2
32,2
31,2
32,2
33,2
31,2
32,2
33,2

and I did this analysis:
lm(GENE-LEVEL~GROUP)
using the GROUP as integer and not as level.

Is it correct? and if the relationship is not strictly linear, ie the second treatment level is not the double of the first treatment, is this analysis still good?
Mainly I would only check whether group0<group1<group2 (or viceversa group0>group1>group2)

Thank you
Michele Pinelli



Michele Pinelli, MD, PhD
Complex Disease Genetics Unit
Department of Cellular and Molecular Biology and Pathology "L. Califano" University "Federico II", Naples
Italy
michele.pinelli_at_unina.it
Skype: dr.sson (Michele Pinelli/Naples, IT)

"People still respect science and technology. There is a problem however. They have no idea what science is."
by Alan Leshner,
CEO of the American Association for the Advancement of Science

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