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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 |
Mon, 21 Jan 2013 16:02:10 +0000 |

somersd disease binpred, tdist transf(z)

somersd disease binpred1 binpred2, tdist lincom (binpred1-binpred2)/2

I hope this helps. Best wishes Roger References

http://www.imperial.ac.uk/nhli/r.newson/papers.htm#papers_in_journals 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 21/01/2013 13:25, Pham Ngoc Minh wrote:

Dear Roger, Thank you very much for your helpful suggestion. While I am reading how to use -somersd- package for estimating Youden index, I found -senspec- package convenient to calculate sensitivity (sn) and specificity (sp). However, I'm not sure about programs below are accurate for estimating age-adjusted sn and sp and their subsequent youden index. logit metabo bmi age predict p if e(sample) senspec metabo p, sensitivity(sn) specificity(sp) gen youdenid= sn-(1-sp) egen youdenidmax= max(youdenid) gen distance = sqrt((1-sn)^2 + (1-sp)^2) egen mindistance = min(distance) /* Identify cut-off point */ list sn sp youdenidmax distance bmi if abs(youdenid -youdenidmax)<0.000001 list sn sp youdenid mindistance bmi if abs(distance - mindistance)<0.000001 And evaluating threshold of BMI based on Youden index or shortest distance from the curve to upper-left corner. I'd appreciate your responses to ensure the above commands. sincerely, Pham Ngoc Minh On Mon, Jan 21, 2013 at 1:30 AM, Roger B. Newson <r.newson@imperial.ac.uk> wrote: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 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: Cut-off point for ROC curve using parametric and non-parametric method***From:*Pham Ngoc Minh <phamngocm@gmail.com>

**References**:**st: Cut-off point for ROC curve using parametric and non-parametric method***From:*Pham Ngoc Minh <phamngocm@gmail.com>

**Re: st: Cut-off point for ROC curve using parametric and non-parametric method***From:*"Roger B. Newson" <r.newson@imperial.ac.uk>

**Re: st: Cut-off point for ROC curve using parametric and non-parametric method***From:*Pham Ngoc Minh <phamngocm@gmail.com>

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