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Re: st: Cut-off point for ROC curve using parametric and non-parametric method


From   "Roger B. Newson" <r.newson@imperial.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Cut-off point for ROC curve using parametric and non-parametric method
Date   Sun, 20 Jan 2013 16:30:46 +0000

If your aim is to estimate the Youden index, then you can use the -somersd- package, which you can download from SSC. The Youden index is an alternative name for Somers' D between 2 binary variables. The -somersd- package can also be used, together with -lincom-, to calculate the difference between 2 Youden indices for 2 diagnostic tests for the same disease.

I hope this helps.

Best wishes

Roger

Roger B Newson BSc MSc DPhil
Lecturer in Medical Statistics
Respiratory Epidemiology and Public Health Group
National Heart and Lung Institute
Imperial College London
Royal Brompton Campus
Room 33, Emmanuel Kaye Building
1B Manresa Road
London SW3 6LR
UNITED KINGDOM
Tel: +44 (0)20 7352 8121 ext 3381
Fax: +44 (0)20 7351 8322
Email: r.newson@imperial.ac.uk
Web page: http://www.imperial.ac.uk/nhli/r.newson/
Departmental Web page:
http://www1.imperial.ac.uk/medicine/about/divisions/nhli/respiration/popgenetics/reph/

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

On 19/01/2013 03:38, Pham Ngoc Minh wrote:
Dear Statalist,

I want to construct age-adjusted (age is a continuous variable) optimal
cut-off points for body mass index (bmi)  and waist circumference (wc) in
determining metabolic syndrome (metabo) for a large study. My question is
how can I calculate sensitivity and specificity for bmi and wc with
adjustment for age, based on which I can calculate Youden index. For
non-parametric method, I know only about using command: roctab metabo bmi,
detail or senspec metabo bmi, se(varname1) spe(varname2)  (without
covariate adjustment). Moreover, how can I calculate age-adjusted
sensitivity and specificity using parametric ROC analysis. It is because
  using non-parametric method showed P less than 0.01, although AUC for
bmi and wc was somewhat similar.
Thank you for your guidance in advance.

Pham Ngoc Minh
Thai Nguyen University Faculty of Public Health, Vietnam
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