Re: st: meta-analysis for diagnostic test

[Roger Newson <roger.newson@kcl.ac.uk>]

At 14:10 12/06/03 -0400, crisasi@aecom.yu.edu wrote:
> How can I perform a meta-analysis for a diagnostic test? I'd like to 
> calculate
> the summary ROC.
> Thanks
I would use the -somersd- package, downloadable from SSC. If X is the 
disease indicator and Y is the quantitative diagnostic test variable, then 
Somers' D of Y with respect to X (D(Y|X)) is related to the ROC area A by 
the formula

D(Y|X)-2*A-1

The -somersd- package saves the estimates and covariance matrices of 
Somers' D as estimation results. Therefore, you could calculate a Somers' D 
and its variance for each of the individual studies, extract the estimates 
vextor and variance matrix for each Somers' D, concatenate the estimates 
vectors for the individual studies to form a vector of Somers' D estimates, 
create a diagonal matrix of the variances of the individual studies, use 
-estimates store- to store these as the current estimation results, and 
then use -lincom- to get a confidence interval for whatever weighted mean 
of the individual study Somers' D values you wanted, and convert that 
confidence interval to a confidence interval for the weighted mean ROC area.

A reference on Somers' D and ROC areas is my Stata Journal article on the 
subject (Newson, 2002). A pre-publication draft of this can be downloaded 
from my website at

http://www.kcl-phs.org.uk/rogernewson/

which also contains manuals for the -somersd- package. It can be accessed 
either using a browser or using the -net- command in Stata.

I hope this helps.

Best wishes

Roger

References

Newson R. Parameters behind "nonparametric" statistics: Kendall's tau, 
Somers' D and median differences. The Stata Journal 2002; 2(1): 45-64.


--
Roger Newson
Lecturer in Medical Statistics
Department of Public Health Sciences
King's College London
5th Floor, Capital House
42 Weston Street
London SE1 3QD
United Kingdom

Tel: 020 7848 6648 International +44 20 7848 6648
Fax: 020 7848 6620 International +44 20 7848 6620
  or 020 7848 6605 International +44 20 7848 6605
Email: roger.newson@kcl.ac.uk
Website: http://www.kcl-phs.org.uk/rogernewson

Opinions expressed are those of the author, not the institution.

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