Message-ID: <20040120112131.4da851f5.feh3k@spamcop.net>
Date: 2004-01-20T16:21:31Z
From: Frank E Harrell Jr
Subject: avas and ace
In-Reply-To: <008701c3df6a$f59c6260$50421bc2@frat>
On Tue, 20 Jan 2004 17:34:24 +0200
f?rat ?zdemir <firat.ozdemir at deu.edu.tr> wrote:
> Hi,
> Does any one know how we can decide on the correct transformation in
> (avas and ace) after having drawn the graphs y,g(y) x ,s(x) and g(y)
> ,s(x) . Is it possible by only looking at patterns the graphs follow for
> example when y ,g(y) shows a logaritmic pattern can we say that log
> transform on y is suitable? Thanks for your help.
> Regards
>
The strategy I use is to not try to do this. One reason is that you may
be tempted to fit a parametric model with such simple transformations,
without accounting for the hidden degrees of freedom from the uncertainty
in estimating the transformations. The areg.boot function in the Hmisc
package will give you bootstrap confidence bands for ace and avas
transformations, taking into account almost all sources of uncertainty.
---
Frank E Harrell Jr Professor and Chair School of Medicine
Department of Biostatistics Vanderbilt University