Re: st: Population attributable fractions (PAFs) in discrete-time survival analysis. -punaf-

["Roger B. Newson" <r.newson@imperial.ac.uk>]

PS "goof idea" should have been "good idea".

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 22/07/2013 11:59, Roger B. Newson wrote:
> I said it is a goof idea to use -punaf- after -cloglog-, but probably
> not a good idea to use -punafcc- after -cloglog-. This is because, in a
> cohort or cross-sectional study, or even in a discrete-time survival
> analysis, we want to estimate a PUF (ie a between-scenario ratio between
> means, which includes proportions), and subtract it and its confidence
> limits from 1 to get a CI for a PAF. The Greenland-Drescher PUF in a
> case-control study, or my definition of a PUF for continuous-time
> survival data modelled using Cox regression, is a mean ratio (eg a mean
> odds ratio for cases or a mean hazard ratio for deaths), which is not
> the same thing as a ratio between means. So, if you wanted a ratio
> between means, then you should use -punaf- (which estimates ratios
> between means), and not -punafcc- (which estimates mean ratios).
>
> 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 22/07/2013 10:43, S.Jenkins@lse.ac.uk wrote:
> > As part of his reply to Angelo Belardi <angelo.belardi@unibas.ch>,
> > Roger Newson <r.newson@imperial.ac.uk> wrote:
> >
> > > A. You can indeed use -punaf- after -cloglog-. (Or you should be able to
> > > do so - let me know if you have any problems.) However, the
> > > interpretation of the attributable and unattributable fractions will
> > > then be similar to the interpretation of these parameters when you use
> > > - -punaf- after -logit- or -logistic-. It is probably not a good idea to
> > > use -punafcc- after -cloglog-. And -punafcc- should probably not be used
> > > after -logit- or -logistic-, except if your data are from a case-control
> > > study (for which -punafcc- was written). After a Cox regression, you may
> > > use either -punaf- or -punafcc-, depending on what kind of population
> > > unattributable and attributable fractions you wanted to estimate (ie my
> > > kind or Samuelson and Eider's kind).
> >
> > My understanding is that Angelo is using -cloglog- to fit the
> > discrete-time  proportional hazard model, i.e. the analogue of the Cox
> > model - which is for continuous survival times -- for interval
> > -censored survival time data. The estimated coefficients on the
> > predictors from the -cloglog- model are exactly the coefficients from
> > the underlying continuous time model, and exp(coeff) is the
> > corresponding hazard ratio.
> > Given this context, why is it not a good idea to use -punaf- after
> > -cloglog-? Could you please clarify?
> >
> > Stephen
> > ------------------
> > Stephen P. Jenkins <s.jenkins@lse.ac.uk>
> >
> > Please access the attached hyperlink for an important electronic
> > communications disclaimer: http://lse.ac.uk/emailDisclaimer
> >
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