R help - Sep 2010 - general question on binomial test / sign test

hello,

i did several binomial tests and noticed for one sparse dataset that
binom.test(1,1,0.5) gives a p-value of 1 for the null, what i can't quite
grasp. that would say that the a prob of 1/2 has p-value of 0 ?? - i must be
wrong but can't figure out the right interpretation..

best,
kay


  


-----
------------------------
Kay Cichini
Postgraduate student
Institute of Botany
Univ. of Innsbruck
------------------------

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Try thinking this one through from first principles, you are essentially saying
that your null hypothesis is that you are flipping a fair coin and you want to
do a 2-tailed test.  You then flip the coin exactly once, what do you expect to
happen?  The p-value of 1 just means that what you saw was perfectly consistent
with what is predicted to happen flipping a single time.

Does that help?

If not, please explain what you mean a little better.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Kay Cichini
> Sent: Wednesday, September 01, 2010 3:06 PM
> To: r-help at r-project.org
> Subject: [R] general question on binomial test / sign test
> 
> 
> hello,
> 
> i did several binomial tests and noticed for one sparse dataset that
> binom.test(1,1,0.5) gives a p-value of 1 for the null, what i can't
> quite
> grasp. that would say that the a prob of 1/2 has p-value of 0 ?? - i
> must be
> wrong but can't figure out the right interpretation..
> 
> best,
> kay
> 
> 
> 
> 
> 
> -----
> ------------------------
> Kay Cichini
> Postgraduate student
> Institute of Botany
> Univ. of Innsbruck
> ------------------------
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/general-
> question-on-binomial-test-sign-test-tp2419965p2419965.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at 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.

David,

The original poster was not looking at distributions and testing distributions,
I referred to the distribution of the p-value to help them understand (in
reference to the paper mentioned).

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: David Winsemius [mailto:dwinsemius at comcast.net]
> Sent: Thursday, September 02, 2010 12:12 PM
> To: Greg Snow
> Cc: Kay Cecil Cichini; ted.harding at manchester.ac.uk; r-help at r-
> project.org
> Subject: Re: [R] general question on binomial test / sign test
> 
> 
> On Sep 2, 2010, at 2:01 PM, Greg Snow wrote:
> 
> <snipped much good material>
> >
> > The real tricky bit about hypothesis testing is that we compute a
> > single p-value, a single observation from a distribution, and based
> > on that try to decide if the process that produced that observation
> > is a uniform distribution or something else (that may be close to a
> > uniform or very different).
> 
> My friendly addition would be to point the OP in the direction of
> using qqplot() for the examination of distributional properties rather
> than doing any sort of hypothesis testing. There is a learning curve
> for using that tool, but it will pay off in the end.
> 
> --
> David.
> >
> > Hope this helps,
> >
> > --
> > Gregory (Greg) L. Snow Ph.D.
> > Statistical Data Center
> > Intermountain Healthcare
> > greg.snow at imail.org
> > 801.408.8111
> >
> >
> >> -----Original Message-----
> >> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> >> project.org] On Behalf Of Kay Cecil Cichini
> >> Sent: Thursday, September 02, 2010 6:40 AM
> >> To: ted.harding at manchester.ac.uk
> >> Cc: r-help at r-project.org
> >> Subject: Re: [R] general question on binomial test / sign test
> >>
> >>
> >> thanks a lot for the elaborations.
> >>
> >> your explanations clearly brought to me that either
> >> binom.test(1,1,0.5,"two-sided") or binom.test(0,1,0.5)
giving a
> >> p-value of 1 simply indicate i have abolutely no ensurance to
reject
> >> H0.
> >>
> >> considering binom.test(0,1,0.5,alternative="greater")
and
> >> binom.test(1,1,0.5,alternative="less") where i get a
p-value of 1
> and
> >> 0.5,respectively - am i right in stating that for the first
estimate
> >> 0/1 i have no ensurance at all for rejection of H0 and for the
> second
> >> estimate = 1/1 i have same chance for beeing wrong in either
> >> rejecting
> >> or keeping H0.
> >>
> >> many thanks,
> >> kay
> >>
> >>
> 
> David Winsemius, MD
> West Hartford, CT