David
On Nov 5, 2011, at 10:43 AM, Frank Harrell <f.harrell at vanderbilt.edu> wrote:
> Just to address a piece of this - in the case in which you are currently
> focusing on only one quantile, the rms package can help by fitting
> restricted cubic splines for covariate effects, and then run anova to test
> for nonlinearity (sometimes a dubious practice because if you then remove
> nonlinear terms you are mildly cheating).
>
> require(rms)
> f <- Rq(y ~ x1 + rcs(x2,4), tau=.25)
> anova(f) # tests associations and nonlinearity of x2
>
> Frank
>
> Julia Lira wrote:
>>
>> Dear all,
>>
>> I would like to know whether any specification test for linear against
>> nonlinear model hypothesis has been implemented in R using the quantreg
>> package.
>>
>> I could read papers concerning this issue, but they haven't been
>> implemented at R. As far as I know, we only have two specification tests
>> in this line: anova.rq and Khmaladze.test. The first one test equality and
>> significance of the slopes across quantiles and the latter one test if the
>> linear specification is model of location or location and scale shift.
>>
>> Do you have any suggestion?
>>
>> Thanks a lot!
>>
>> Best regards,
>>
>> Julia
>>
>> [[alternative HTML version deleted]]
>>
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>>
>
>
> -----
> Frank Harrell
> Department of Biostatistics, Vanderbilt University
> --
> View this message in context: http://r.789695.n4.nabble.com/linear-against-nonlinear-alternatives-quantile-regression-tp3993327p3993416.html
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>
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