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Re: st: RE: broken stick (piecewise linear) regression


From   keith Farnsworth <k.farnsworth@qub.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: broken stick (piecewise linear) regression
Date   Tue, 24 May 2005 13:13:20 +0100

Thanks, Nick, but I looked at mkspline before and realised that it specifically requires the knot point, whereas the problem I have, addressed by Bacon and Watts, is to find the best fit knot point i.e - estimating the transition between two intersecting straight lines. Unless there is something you can do with mkspline that is not in the documentation, I don't see that it can fit the knot.

Any other idea?


Keith.

On Tuesday, May 24, 2005, at 12:55 Europe/Dublin, Nick Cox wrote:


. search mkspline

should help. See both entries.

Nick
n.j.cox@durham.ac.uk

keith Farnsworth

I intend to fit a broken stick model following Bacon and Watts
"Estimating the transition between two intersecting straight lines",
Biometrika 1971. I have seen code for this to use the S or R
package's
nls, which I suspect uses maximum likelihood (but not sure) [see
http://www.biostat.wustl.edu/archives/html/s-news/2000-04/
msg00215.html].

I am not an S user, I am a Stata enthusiast!
However, I found no reference to this kind of model in Stata
searches.
I hope someone with more experience than me can explain how
Stata will
implement the Bacon and Watts model.
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Dr Keith Farnsworth
Lecturer in Mathematical and Behavioural Ecology
Queens University Belfast

Medical Biology Centre
97 Lisburn Road
Belfast BT9 7BL
Northern Ireland
phone +44 (0)2890 272352
fax       +44 (0)2890 236505

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