by definition, the one tailed p-value has to be <= 0.5 so there is
still something wrong with your OpenEpi calc. Most likely it's
calculating the
2 tailed p-value and then mistakenly multiplying by 2. For example:
A) Suppose you are testing
Ho: u = u_0
H1 u > u_0
and your t-stat was -0.3 Then prob( T > t_0) = 0.62 so your pvalue
would be 0.62.
B) Instead, suppose you are testing
Ho: u = u_0
H1 u != u_0
and your t-stat was -0.3. Then, one calculates, prob(T < t_0 = -.3) =
.31 and then multiplies by 2 ( because the test is 2 sided ) so the
pvalue is still 0.62.
So, it's probably doing the first case andf them multiplying it by 2
which is incorrect. Also, no offense intended but it's dangerous to use
these things
unless the understanding is there. In fact, it can be dangerous to use
them even when the understanding is there !!!!!!! Peter Daalgard's book
or John Verzani's book are probably decent recommendations to read for
the above kind of thing but an introduction to statistical testing
textbook is probably most useful. I can't think of a title at the
moment.
On Sat, Mar 21, 2009 at 9:07 PM, C.H. wrote:
I tried the OpenEpi, the p-value of 1.25 is due to the fact that the
one tailed p-value is 0.62. The two tailed p-value then is 0.62 * 2 =
1.25. OpenEpi is not clever enough to ceiling the p-value to 1.
CH
On Sun, Mar 22, 2009 at 3:43 AM, David Winsemius
<dwinsem...@comcast.net> wrote:
Let me ask you: What degree of credibility should be accorded a WWW
application that delivers a p-value of 1.25?
If the answer is not immediately and glaringly obvious, then tell us,
what
sort of axioms of probability are you working with?
--
David Winsemius
On Mar 21, 2009, at 3:17 PM, Viju Moses wrote:
Hi, I noted a discrepancy between R and openepi when I ran a fisher
test
with the same matrix. In R:
a=matrix(c(1,2,6,17), nrow=2)
a
[,1] [,2]
[1,] 1 6
[2,] 2 17
fisher.test(a, conf.int=T)
Fisher's Exact Test for Count Data
data: a
p-value = 1
alternative hypothesis: true odds ratio is not equal to 1
95 percent confidence interval:
0.02061498 31.73691924
sample estimates:
odds ratio
1.396646
But in openepi the P value is 1.25. (In another instance too for
other
sets of data, I had got a p value of 1 in 3 instances for a
prop.test when I
got 3 other answers on a friend's stata software with the same data.
)
I'm using R on Ubuntu Intrepid. Is there anything I'm doing wrong?
Any
other packages I have to install?
Thanks in advance
Viju Moses
______________________________________________
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.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
______________________________________________
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.
--
CH Chan
Research Assistant - KWH
http://www.macgrass.com
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
______________________________________________
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.
