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st: New version of -somersd- on SSC

From   "Roger B. Newson" <>
To   "" <>
Subject   st: New version of -somersd- on SSC
Date   Wed, 06 Jun 2012 11:27:07 +0100

Thanks as always to the services of Kit Baum, who seems on this occasion to have updated SSC when absent from Boston, a new version of the -somersd- is now available for download from SSC. In Stata, use the -ssc- command to do this, or -adoupdate- if you already have an old version of -somersd-.

The -somersd- package is described as below on my website. The new version has been updated to Stata Version 12. It also fixes a rarely-encountered bug, which caused -somersd- to fail when Somers' D was calculated as being slightly greater than 1 or slightly less than -1, as in 1+1e-16 or -1-1e-16. This occasionally used to happen when sampling probability weights were used, in spite of using double or quadruple precision in Mata. The new version rounds values of Somers' D down to 1 if greater than 1 or up to -1 if less than -1, so the bug is now fixed. I would like to thank Kerry Kammire of Stata Technical Support for her very helpful advice that fixing Mata bugs in a .mlib file necessitates either a version upgrade or access to an earlier version of Stata.

Users of earlier versions of Stata can still download the Stata Version 5, 6, 9 or 10 versions of -somersd- from my website by typing, in Stata,

net from "";

and selecting the subdirectory for the most recent Stata version compatible with their own, and installing the appropriate version of -somersd-.

Best wishes


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
Tel: +44 (0)20 7352 8121 ext 3381
Fax: +44 (0)20 7351 8322
Web page:
Departmental Web page:

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

package somersd from

      somersd: Kendall's tau-a, Somers' D and percentile slopes

The somersd package contains the programs somersd, censlope and cendif,
      which calculate confidence intervals for a range of parameters behind
      rank or "nonparametric" statistics. somersd calculates confidence
      intervals for generalized Kendall's tau-a or Somers' D parameters,
and stores the estimates and their covariance matrix as estimation results.
      It can be used on left-censored, right-censored, clustered and/or
stratified data. censlope is an extended version of somersd, which also calculates confidence limits for the generalized Theil-Sen median slopes (or other percentile slopes) corresponding to the version of Somers' D
      or Kendall's tau-a estimated. cendif is an easy-to-use program to
      calculate confidence intervals for Hodges-Lehmann median differences
(or other percentile differences) between two groups. The somersd package
      can be used to calculate confidence intervals for a wide range of
      rank-based parameters, which are special cases of Kendall's tau-a,
      Somers' D or percentile slopes. These parameters include differences
between proportions, Harrell's c index, areas under receiver operating characteristic (ROC) curves, differences between Harrell's c indices or
      ROC areas, Gini coefficients, population attributable risks, median
      differences, ratios, slopes and per-unit ratios, and the parameters
      behind the sign test and the Wilcoxon-Mann-Whitney or Breslow-Gehan
ranksum tests. Full documentation of the programs (including methods and formulas) can be found in the manual files somersd.pdf, censlope.pdf and
      cendif.pdf, which can be viewed using the Adobe Acrobat Reader.

      Author: Roger Newson
      Distribution-date: 30may2012
      Stata-version: 12

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