# R: [R] one-sample binomial test

Guazzetti Stefano Stefano.Guazzetti at ausl.re.it
Sat Jul 6 07:58:07 CEST 2002

```try
?power.prop.test

> -----Messaggio originale-----
> Da: Tim Wilson [mailto:wilson at visi.com]
> Inviato: sabato 6 luglio 2002 6.05
> A: R-help
> Oggetto: [R] one-sample binomial test
>
>
> Hi everyone,
>
> Here's how I solved a problem for my stats class. I'm pretty sure I
> understand what's going on, but I wonder if there's a more
> direct way to
> solve it.
>
> Problem summary:
>
> A recent poll indicated that Candidate A is leading B with 55% of the
> vote. How many voters need to be surveyed to ensure a margin
> of error of
> +/- 2.5% with 99% confidence.
>
> Here's what I did:
>
> > binom.test(55, 100, 0.5, alternative='t', conf.level=0.99)
>
>         Exact binomial test
>
> data:  55 and 100
> number of successes = 55, number of trials = 100, p-value =
> 0.3682
> alternative hypothesis: true probability of success is not equal
> to 0.5
> 99 percent confidence interval:
>  0.4170382 0.6780727
> sample estimates:
> probability of success
>                   0.55
>
> After some trial and error I got:
>
> > binom.test(1100, 2000, 0.5, alternative='t', conf.level=0.99)
>
>         Exact binomial test
>
> data:  1100 and 2000
> number of successes = 1100, number of trials = 2000, p-value =
> 8.457e-06
> alternative hypothesis: true probability of success is not equal
> to 0.5
> 99 percent confidence interval:
>  0.5210033 0.5787563
> sample estimates:
> probability of success
>                   0.55
>
> So my answer is that you would need to survey more than 2000
> persons. Is
> there a way other than trial and error to solve this?
>
> -Tim
>
> --
> Tim Wilson      |   Visit Sibley online:   | Check out:
> Henry Sibley HS |  http://www.isd197.org   | http://www.zope.com
> W. St. Paul, MN |                          | http://slashdot.org
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