On 10 Apr 2014, at 16:49 , Alwina Hermann <alwina.herm...@1plusi.de> wrote:
> Dear R team, > > I'm not sure if I use the right distribution list, but I hope in case if > not, you will forward it to the reference person. > > Following problem occured: > I used R to calculate the p-value for the two sided binomial test (exact - > Pearson). > For a very little difference for my forecast I get a very big difference in > my p-value > > > binom.test(1,101, 0.02402) > > Exact binomial test > > data: 1 and 101 > number of successes = 1, number of trials = 101, p-value = 0.7375 > alternative hypothesis: true probability of success is not equal to 0.02402 > 95 percent confidence interval: > 0.00025064 0.05393235 > sample estimates: > probability of success > 0.00990099 > >> binom.test(1,101, 0.02403) > > Exact binomial test > > data: 1 and 101 > number of successes = 1, number of trials = 101, p-value = 0.5243 > alternative hypothesis: true probability of success is not equal to 0.02403 > 95 percent confidence interval: > 0.00025064 0.05393235 > sample estimates: > probability of success > 0.00990099 > > > Can you please explain where this huge difference come from? > Which mathematical explanation is given for this topic? Check the definition of the p value (you need to study the source for that, I suppose). It's the probability of getting an observation with a point probability less than or equal to that of the observed value. The crucial bit is whether the point probability p(1) is less than or bigger than p(3): > dbinom(0:4,101, 0.02403) [1] 0.08572022 0.21316798 0.26242746 0.21322618 0.12862456 > dbinom(0:4,101, 0.02402) [1] 0.08580898 0.21329771 0.26247520 0.21317403 0.12853828 I.e., in the first case, X==3 is not counted into the p-value, whereas it is in the second case. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.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.