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st: New package -punafcc- for SSC

From   "Roger B. Newson" <>
To   "" <>
Subject   st: New package -punafcc- for SSC
Date   Mon, 31 Oct 2011 11:59:59 +0000

Thanks as always to Kit Baum, a new package -punafcc- is now available for download from SSC. In Stata, use the -ssc- command to do this.

The -punafcc- command is described as below on my website, and estimates population unattributable and attributable fractions for case-control or survival studies after a logistic or Cox regression model has been fitted. It currently has the limitation that it cannot do this if the model contains factor interactions involving the exposure of interest, which varies between scenarios. However, there are work-arounds to solve this problem, and these are discussed in the on-line help. (I hope to revisit this issue in future.)

I would like to thank all at StataCorp for providing the very impressive -margins- command that made -punafcc- possible. I would particularly like to thank Kristin MacDonald, Jennifer Rolfes, Miguel Dorta and Jeff Pitblado, who have all helped me (very patiently) with my complicated and very demanding -margins- queries arising from the development of -punafcc- and -punaf-.

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 punafcc from

punafcc: Population attributable fractions for case-control and survival studies

      punafcc calculates confidence intervals for population attributable
      and unattributable fractions in case-control or survival studies.
      punafcc can be used after an estimation command whose parameters are
      interpreted as log rate ratios, such as logit or logistic for
      case-control data, or stcox for survival data.  It estimates the log
      of the mean rate ratio, in cases or deaths, between 2 scenarios, a
      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.  This ratio
      is known as the population unattributable fraction (PUF), and is
      subtracted from 1 to derive the population attributable fraction
      (PAF), defined as the proportion of the cases or deaths attributable
      to living in Scenario 0 instead of Scenario 1.

      Author: Roger Newson
      Distribution-Date: 28october2011
      Stata-Version: 12

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