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Re: st: Sample size determination for ROC comparison


From   Joseph Coveney <jcoveney@bigplanet.com>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Sample size determination for ROC comparison
Date   Thu, 15 Apr 2004 00:43:44 +0900

I think that this can be done in Stata using -simulate-.  Samples of various 
sizes with given areas under the reciever operating characteristic curves could 
be created with -drawnorm outcome predictor, corr(1 `rho' \ `rho' 1) 
n(`sample_size')-.  Then -replace outcome = outcome > 0.5-, and -replace- the 
predictor according to the assumption for its distribution.  (For a normally 
distributed predictor, AUC given by -lroc- after -probit outcome predictor- is 
(`rho' + 1) / 2).  Create two such samples (one for each of the two indepedent-
sample comparison groups) with their given AUCs determined by their respective 
`rho' values used in -drawnorm-, and -append- them, using a grouping indicator 
variable to tell them apart and to reference in the  -by- option in -roccomp-.  
Power to discriminated the two groups at each sample size and level of Type I 
error rate can then be estimated based upon the results returned from 
-roccomp-, with the number of replications determined by the precision desired 
for the power estimate.

Joseph Coveney

-------------------------------------------------------------------------------

Gregory Daniel wrote:

> Dear Statlist,
> 
> I am using -roccomp- to compare areas under the ROC curve estimated from
> two independent samples.  Can anyone point me in the right direction for
> appropriate power and sample size calculations for this test?
> 
> Greg
>  


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