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Re: st: RE: qreg versus rreg


From   Richard Williams <[email protected]>
To   [email protected]
Subject   Re: st: RE: qreg versus rreg
Date   Fri, 30 Jan 2004 09:43:10 -0500

At 01:58 PM 1/30/2004 +0000, Nick Cox wrote:
My experience loosely matches Richard's, certainly
in terms of wanting to think that -qreg- is as good
because of the much greater ease in explaining it.
At the same time, if you have outliers everywhere,
you are possibly working on inappropriate scales
and should wonder about reaching for a transformation
or, in some frameworks, a different link function.
My inclination would be to stress that either program should probably be a last resort, rather than a first. Outlier problems are often just a result of coding errors, e.g. you left a zero out, or you didn't handle missing data codes right. Or, the problem may be model specification: add another variable or two and maybe the outlier isn't such an outlier any more. I preach similar things with regards to heteroskedasticity. Don't just immediately jump to WLS or something like that. Subgroup differences in variable effects might produce a pattern of heteroskedacity, but adding interaction terms may make that go away.

But, there is still the issue of what to do when the outliers really really are legitimate! I remember reading a complaint once that, if statisticians ruled the natural sciences, Pluto would have been tossed out as an outlier and we'd have never come up with some of the modern theories of gravity and physics.

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Richard Williams, Notre Dame Dept of Sociology
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