[R] avas and ace

Frank E Harrell Jr feh3k at spamcop.net
Tue Jan 20 17:21:31 CET 2004

On Tue, 20 Jan 2004 17:34:24 +0200
fýrat özdemir <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

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