# Re: st: RE: RE: probability question

 From Richard Goldstein To statalist@hsphsun2.harvard.edu Subject Re: st: RE: RE: probability question Date Wed, 28 Oct 2009 13:15:23 -0400

```thank you -- that's quite interesting and means I did not think things
through sufficiently when I replied to Paul -- sorry about that

Edgar Munoz wrote:
> I like this approach using tabi as a calculator for this.
>
> r(p_exact) is P(n11 >= 3), the p-value in the Fisher's exact test
>
> if we calculate P(n11 >= 4), we can obtain P(n11 = 3) by difference
>
>
> . tabi 4 0 \ 3 113, exact
>
>            |          col
>        row |         1          2 |     Total
> -----------+----------------------+----------
>          1 |         4          0 |         4
>          2 |         3        113 |       116
> -----------+----------------------+----------
>      Total |         7        113 |       120
>
>            Fisher's exact =                 0.000
>    1-sided Fisher's exact =                 0.000
>
> . return list
>
> scalars:
>            r(p1_exact) =  4.26072210718e-06
>             r(p_exact) =  4.26072210718e-06
>                   r(c) =  2
>                   r(r) =  2
>                   r(N) =  120
>
>
>      |  p3exact     p3plus     p4plus |
>      |--------------------------------|
>   1. | .0004815   .0004857   4.26e-06 |
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Visintainer PhD,
> Paul
> Sent: Wednesday, October 28, 2009 7:49 AM
> To: 'statalist@hsphsun2.harvard.edu'
> Subject: st: RE: probability question
>
> I'm probably thinking of this too simplistically, but wouldn't this just be
> a Fisher's exact test?
>
>
> . tabi 3 1 \ 4 112, exact   /* where col = rain and row = hat */
>
>            |          col
>        row |         1          2 |     Total
> -----------+----------------------+----------
>          1 |         3          1 |         4
>          2 |         4        112 |       116
> -----------+----------------------+----------
>      Total |         7        113 |       120
>
>            Fisher's exact =                 0.000
>    1-sided Fisher's exact =                 0.000
>
> . return list
>
> scalars:
>            r(p1_exact) =  .0004857223202188
>             r(p_exact) =  .0004857223202188
>                   r(c) =  2
>                   r(r) =  2
>                   r(N) =  120
>
>
> ___________________________________
> Paul F. Visintainer, PhD
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Richard Goldstein
> Sent: Wednesday, October 28, 2009 8:38 AM
> To: statalist
> Subject: st: probability question
>
> it's been a long time since I thought about questions like this, but, as
> a lead-in to a study, a client has asked the following question which he
> thinks he understands and says is related to where he wants to go:
>
> during a consecutive period of 120 days, if it rains on 7 days and my
> client wears a hat on 4 days (these are independent of any knowledge of
> the weather), what is the probability that it will rain on 3 of the days
> on which he is wearing a hat?
>
> my client swears that this is not a homework problem for him or his wife
> or one of their kids!
>
> Rich
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```