[R] binom.test

(Ted Harding)
Thu, 19 Oct 2006 15:53:23 -0000

On 19-Oct-06 Ethan Johnsons wrote:
> R-experts:
>
> A quick question, please.
>
>>From a lab exp, I got 12 positives out of 50.
> To get 90% CI for this , I think binom.test might be
> the one to be used.
> Is there a better way or function to calculate this?

What do you mean by "better"? For a symmetrical 2-sided
exact binomial confidence interval, binom.test gives the
result quickly and, to within the precision of pbinom,
correctly (as I've just verified by hand!).

And you can get 1-sided CIs by setting the 'alternative'
option, or asymmetrical CI's by finding the two 1-sided
CIs (e.g. for conf.level = 0.03 and 0.07) that you want.

What do you want to improve on?

>> binom.test(x=12, n=50, p=12/50, conf.level = 0.90)
>
>         Exact binomial test
>
> data:  12 and 50
> number of successes = 12, number of trials = 50, p-value = 1
> alternative hypothesis: true probability of success is not equal to
> 0.24
> 90 percent confidence interval:
>  0.1447182 0.3596557

  r<-12 ; n<-50

  1-pbinom(r-1,n, 0.14471815)
  [1] 0.04999999

  1-pbinom(r-1,n, 0.14471816)
  [1] 0.05000001


  pbinom(r,n, 0.35965569)
  [1] 0.05000001

  pbinom(r,n, 0.35965570)
  [1] 0.05

  pbinom(r,n, 0.35965571)
  [1] 0.04999998


> sample estimates:
> probability of success
>                   0.24
>
> thx much
>
> ej

Best wishes,
Ted.

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Date: 19-Oct-06                                       Time: 16:53:19
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