[R] nls, nlrq, and box-cox transformation

[Philippe Grosjean]

>Dear r-help members
>I posted this message already yesterday, but don't know whether it
>reached you since I joined the group only yesterday.
>I would like to estimate the boxcox transformed model
> (y^t - 1)/t ~ b0 + b1 * x.
>Unfortunately, R returns with an error message when I try to
>perform this with the call
>nls( I((y^t - 1)/t) ~ I(b0 + b1*x),
>	start = c(t=1,b0=0,b1=0), data = mydataframe)

>The error message is:  Object "t" not found

>Apparently R seems not to accept parameters on the left hand
>side of a regression model. I know that my do-it-yourself
>strategy is not necessary, since the package box-cox is
>available. Unfortunately, I want the use the box-cox
>transformation in a quantile regression, i.e. I have to replace
>nls by nlrq in the call above.

>Any suggestions?

>Thanks and best regards,
>	Johannes Ludsteck

You suggest the solution yourself: transform the equation to have all
parameters at the right, thus:

y ~ ((b0 + b1 * x) * t + 1) ^ 1/t

(double check if this is correct)

Best,

Philippe Grosjean

...........]<(({?<...............<?}))><...............................
 ) ) ) ) )
( ( ( ( (       Dr. Philippe Grosjean
 ) ) ) ) )
( ( ( ( (       Numerical Ecology Laboratory
 ) ) ) ) )      Mons-Hainaut University
( ( ( ( (       8, Av. du Champ de Mars, 7000 Mons
 ) ) ) ) )      Belgium
( ( ( ( (
 ) ) ) ) )      e-mail: phgrosjean at sciviews.org
( ( ( ( (       SciViews project coordinator (http://www.sciviews.org)
 ) ) ) ) )
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