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st: New version of -punaf- on SSC

From   "Roger B. Newson" <>
To   "" <>
Subject   st: New version of -punaf- on SSC
Date   Thu, 27 Oct 2011 16:02:51 +0100

Thanks as always to Kit Baum, a new version of the -punaf- package 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 -punaf-.

The -punaf- package is described as below on my website. The new version fixes a bug, which caused -punaf- always to calculate Normal confidence intervals for the population unattributable fraction (PAF), even when the confidence intervals for the population unattributable fraction (PUF) were calculated using the t-distribution. This bug is not often encountered, as binomial models usually do not use the t-distribution. However, the t-distribution is used when the binomial regression command (eg -logit-) is called with the -svy:- prefix and the user specifies the option -vce(unconditional)- to -punaf- (which passes that option through to -margins-).

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 punaf from

      punaf: Population attributable fractions for cohort studies

      punaf calculates confidence intervals for population attributable
      fractions, and also for scenario means and their ratio, known as
      the population unattributable fraction.  punaf can be used after
      an estimation command whose predicted values are interpreted as
      conditional arithmetic means, such as logit, logistic, poisson,
      or glm.  It estimates the logs of two scenario means, the
      baseline scenario ("Scenario 0") and a fantasy scenario
      ("Scenario 1"), in which one or more exposure variables are
      assumed to be set to particular values (typically zero), and any
      other predictor variables in the model are assumed to remain the
      same.  It also estimates the log of the ratio of the Scenario 1
      mean to the Scenario 0 mean.  This ratio is known as the
      population unattributable fraction, and is subtracted from 1 to
      derive the population attributable fraction, defined as the
      proportion of the mean of the outcome variable attributable to
      living in Scenario 0 instead of Scenario 1.

      Author: Roger Newson
      Distribution-Date: 26october2011
      Stata-Version: 12

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