Statalist The Stata Listserver


[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

Re: R: st: bootstrapping probabilities


From   Maarten buis <[email protected]>
To   [email protected]
Subject   Re: R: st: bootstrapping probabilities
Date   Sun, 8 Apr 2007 09:27:34 +0100 (BST)

--- Carlo Lazzaro <[email protected]> wrote:
> I was dealing with model aimed at comparing two healthcare programmes
> (A and B; 255 observations each) in terms of their effectiveness. 
> I cannot rely on a dataset, but only on a point estimates for A and B
> effectiveness, coming from a clinical trial (programme A=88,89%;
> programme B= 79,76%; difference=9,13%).

The direct answer would be -prtesti 255 .8889 255 .7976-. 

Since you were looking for a bootstrap/simulation kind of approach (and
I like that kind of approach since it is often more intuitive) I have
also wrote a simulation. I am assuming that the proportion is referring
to the proportion of people that have not died, or suffered something
else unpleasant, after having gone through either program A or B, i.e.
the underlying data, that you don't have, are 255 cases for each
program where each case could have either a 0 or a 1. So I randomly
created this data, assuming that the found proportions where the true
population proportions. This generated data would be a random sample
from this `population'. I did so many times (2000) and computed the
difference in `sample' proportions each time, thus creating the
sampling distribution of the difference.

*---------- begin example -----------
capture program drop sim
program define sim, rclass
	drop _all
	set obs 255
	gen byte successA = uniform() < .8889 
	gen byte successB = uniform() < .7976 
	sum successA, meanonly
	scalar A = r(mean)
	sum successB, meanonly
	return scalar diff = A - r(mean)
end
simulate sim diff=r(diff), reps(2000) 

sum diff
centile diff, centile(2.5 97.5)
*---------- end example ----------------
(For more on how to use examples I sent to the Statalist, see:
http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )

Hope this helps,
Maarten

-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------


		
___________________________________________________________ 
To help you stay safe and secure online, we've developed the all new Yahoo! Security Centre. http://uk.security.yahoo.com
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



© Copyright 1996–2024 StataCorp LLC   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index