# [R] Previously attainable fisher's exact test

peter dalgaard pdalgd at gmail.com
Thu Apr 14 09:01:31 CEST 2011

```On Apr 14, 2011, at 01:29 , (Ted Harding) wrote:

> On 13-Apr-11 17:40:53, Jim Silverton wrote:
>> I have a matrix say,
>>
>> 1  4
>> 23  30
>>
>> and I want to find the previously attainable fisher's exact test
>> p-value. Is there a way to do this in R?
>> --
>> Thanks,
>> Jim.
>
> I do not understand what you mean by "previously attainable".
>
> As far as that particular matrix is concerned, the fisher.test()
> function will yield its exact Fisher P-value:
>
>  M <- matrix(c(1, 4, 23, 30), byrow=TRUE, nrow=2)
>  M
>  #      [,1] [,2]
>  # [1,]    1    4
>  # [2,]   23   30
>  fisher.test(M)
>  #         Fisher's Exact Test for Count Data
>  # data:  M
>  # p-value = 0.3918
>  # alternative hypothesis: true odds ratio is not equal to 1
>  # 95 percent confidence interval:
>  #  0.006355278 3.653391412
>  # sample estimates:
>  # odds ratio
>  #  0.3316483
>
> So the P-value is 0.3918 (as attained now, and as attainable
> at any time previously if you had done the above ... !).
>

What Ted said, plus

f <- fisher.test(M)
f\$p.value
# [1] 0.3917553

--
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

```