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: [email protected]
[mailto:[email protected]] On Behalf Of Visintainer PhD,
Paul
Sent: Wednesday, October 28, 2009 7:49 AM
To: '[email protected]'
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: [email protected]
[mailto:[email protected]] 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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