Message-ID: <Pine.LNX.4.44.0305202154020.28023-100000@gannet.stats>
Date: 2003-05-20T20:58:31Z
From: Brian Ripley
Subject: stepAIC
In-Reply-To: <20030520204411.50253.qmail@web41201.mail.yahoo.com>
stepAIC is support software for MASS4. There is an example in the book of
it doing what you claim it cannot do. So do look it up and see what your
mistake was.
On Tue, 20 May 2003, array chip wrote:
> I tried to use stepAIC for a cox proportional model
> (30 independent variables) built by coxph. I found
> that no matter whether I used direction="forward" or
> direction="backward" as an option in stepAIC, I
> alweays got exactly the same output, i.e. it seems
> only backward selection was performed (eliminate 1
> variable at a time). why did it happen like this? or
> for cox model, stepAIC can only perform backward
> selection?
--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595