on 13/02/2003 7:37 am, FUKUGAWA, Nobuya at [email protected]
wrote:
> I want to cut off extraordinarily large and small values from variables
> used in regression analysis.
> What is the easiest way to drop the largest and smallest 1% of observations
> from variables in STATA-7?
These values are potentially very informative. You can try other approaches
such as
- median regression
- intreg
- robust regression
Very large and very small values can indicate problems with measurement.
-intreg- can be used to specify that these values are not known precisely
but are bigger/smaller than some threshold.
Robust regression is useful to confirm that substantive conclusions from
your analysis are not being 'driven' by influential observations.
I hate discarding data. These strange values are trying to tell us
something. We ignore them at our peril. I am analysing some microbiology
data at the moment. There is a tradition of discarding any measurements
where there were so many bugs that the plate was unreadable. You can imagine
the havoc that this has played with results!
Ronan M Conroy ([email protected])
Lecturer in Biostatistics
Royal College of Surgeons
Dublin 2, Ireland
+353 1 402 2431 (fax 2764)
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