Linda,
There are different views about whether someone doing statistical
analysis should first take a certain number of statistics course. I
think for your issue some background information would certainly help.
You have not correctly interpreted the paper. The main point is that
for most cases likely to be seen in practice, the median test is
tantamount to discarding about 1/3 of your animals. The Wilcoxon test
is a good choice for a huge variety of situations. Even if the data are
Gaussian it has efficiency 3/pi whereas the median test has efficiency
2/pi in that case.
Frank
On 05/28/2010 08:58 AM, linda Porz wrote:
Hello,
I can't have different data these data came from mice that have lived under
certain condition in the lab! I have just read the mentioned publication
"Should the median test be retired from general use?" It says in the
conclusion "If one felt that the data could not come from a Cauchy or slash
distribution, the Wilcoxon should be used."! What is this? Is there is any
test in R for a Cauchy or slash distribution? Can I used the unpaired
Wilcoxon, or I have a Cauchy distributed data?
Many thanks,
Linda
2010/5/27 Joshua Wiley<jwiley.ps...@gmail.com>
Hello Linda,
The "problem" is actually the median of your data. What the function
median.test() does first is combine both groups. Look at this:
median(c(group1, group2))
the median is 1, but the lowest value of the groups is also 1. So
when the function does the logical check z< m where z = c(group1,
group2) and m is the median, there are no values that are less than
the median value. Therefore there is only 1 level, and the fisher
test fails.
You would either need different data or adjust the function to be:
fisher.test(z<= m, g)$p.value
that way it's less than or equal to the median.
Hope that helps,
Josh
On Thu, May 27, 2010 at 7:24 AM, linda Porz<linda.p...@gmail.com> wrote:
Hi all,
I have found the following function online
median.test<-function(y1,y2){
z<-c(y1,y2)
g<- rep(1:2, c(length(y1),length(y2)))
m<-median(z)
fisher.test(z<m,g)$p.value
}
in
http://www.mail-archive.com/r-help@r-project.org/msg95278.html
I have the following data
group1<- c(2, 2, 2, 1, 4, 3, 1, 1)
group2<- c(3, 1, 3, 1, 4, 1, 1, 1, 7, 1, 1, 1, 1, 1, 2)
median.test(w1,group1)
[1] 1
median.test(group1,group2)
Error in fisher.test(z< m, g) : 'x' and 'y' must have at least 2 levels
I am very thankful in advance for any suggestion and help.
Regards,
Linda
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PLEASE do read the posting guide
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--
Joshua Wiley
Senior in Psychology
University of California, Riverside
http://www.joshuawiley.com/
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______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Frank E Harrell Jr Professor and Chairman School of Medicine
Department of Biostatistics Vanderbilt University
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