R help - Feb 2009 - Chi-squared test adjusted for multiple comparisons? Harbe's test?

Hi!

I have some data that looks like this
up	down	percentaje
uew_21	20	14	58.82
uew_20_5	27	40	40.29
uew_20	8	13	38.09
uew_19_5	17	42	28.81



So I have 4 experimental conditions and I am counting number of  
animals in the up and down compartment and the calculating the  
percentage, I want to know which one of the conditions is different  
from each other. If the data wouldn't be percentage I would runt a  
kruskal-wallis test to check for general differences and then when  
significan a post-hoc test, comparing differents pairs with Man- 
Whitney (wilcoxon function in R) with a bonferroni correction for  
multiple comparisons. But as the data are in the percentaje form, I  
know I need to analize them with either a chi squared or a g-test, but  
I have no idea if I can do such a test with many comparissons or how  
to do it in R, as well I have seen a paper in which they do something  
similar and they are using a Harber's chi squared test. Does anybody  
know how to do that in R?

Thank you  very much for your help, and thanks to the jim and chuck  
for answering my previous statistical question!

Lucia

	[[alternative HTML version deleted]]

Categorical data analysis is definitely the way you want to go.
Which test you use depends on how you are going to use the results.

For "quick and dirty" I would suggest using Fisher's exact test on
all
2x2 submatricies of counts. In this case, with 4 treatments you have
6 possible 2x2 submatricies. See "fishers.test" function.

Another possibility would be a log-linear model, to model Ln(p/q).

Murray M Cooper, Ph.D.
Richland Statistics
9800 N 24th St
Richland, MI, USA 49083
Mail: richstat at earthlink.net

----- Original Message ----- 
From: "Laura Lucia Prieto Godino" <llp23 at cam.ac.uk>
To: <r-help at r-project.org>
Sent: Thursday, February 05, 2009 7:06 AM
Subject: [R] Chi-squared test adjusted for multiple comparisons? 
Harbe'stest?

> Hi!
>
> I have some data that looks like this
> up down percentaje
> uew_21 20 14 58.82
> uew_20_5 27 40 40.29
> uew_20 8 13 38.09
> uew_19_5 17 42 28.81
>
>
>
> So I have 4 experimental conditions and I am counting number of
> animals in the up and down compartment and the calculating the
> percentage, I want to know which one of the conditions is different
> from each other. If the data wouldn't be percentage I would runt a
> kruskal-wallis test to check for general differences and then when
> significan a post-hoc test, comparing differents pairs with Man-
> Whitney (wilcoxon function in R) with a bonferroni correction for
> multiple comparisons. But as the data are in the percentaje form, I
> know I need to analize them with either a chi squared or a g-test, but
> I have no idea if I can do such a test with many comparissons or how
> to do it in R, as well I have seen a paper in which they do something
> similar and they are using a Harber's chi squared test. Does anybody
> know how to do that in R?
>
> Thank you  very much for your help, and thanks to the jim and chuck
> for answering my previous statistical question!
>
> Lucia
>
> [[alternative HTML version deleted]]
>
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