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Re: st: Correlation b/w independent variables in xtlogit
At 08:28 AM 5/17/2007, Maarten buis wrote:
Centering is another approach to consider. If you center age (i.e.
subtract the mean of age from each case) and then square, centered
age and centered age^2 will generally be less highly correlated than
age and age^2. Things like this (along with rescaling vars) may help
with numerical problems. The bigger advantage may be with regards to
interpretation. Instead of 0 standing for a newborn infant, 0 on
centered age stands for an average-aged person.
Age and age squared will measure something different, so if Stata can
estimate it, the results will make sense. Very high correlation may
cause some numerecial problems. In those cases it is possible to remove
the correlation between these variables using the -orthpoly- command,
see: -help orthpoly-.
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
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