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Re: st: stepwise
At 04:30 AM 9/4/2006, Timothy.Mak@iop.kcl.ac.uk wrote:
Two other quick comments: Since you are also using SPSS, you could
use pairwise deletion of missing data, which might be ok if the data
are missing randomly (but if nonrandom, you've got some problems
regardless of what you do).
stepwise regression is needed. Say we have n = 200, and a potential pool
of predictors = 50, say that each of these 50 predictors have 1 or 2
missing, not necesarily randomly. Using the Stata stepwise procedure, we
Also, if you've got 50 predictors and are using the .05 level of
significance, then just by chance alone you'd expect 2 or 3 vars to
enter in. I'd suggest using the .01 level of significance; or figure
out exactly what alpha level to use by doing, say, a Bonferroni adjustment.
Overall though, I probably wouldn't feel very comfortable with SW in
this case, regardless of how I did it! I'd certainly want to add
some cautionary notes in my writeup, perhaps labeling the analysis as
exploratory and in need of replication in other studies.
I wonder if some of those 50 vars couldn't be combined into a smaller
number of scales? Do you really have 50 unique concepts here, or do
you maybe have several items that tap into the same concept in
slightly different ways?
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
WWW (personal): http://www.nd.edu/~rwilliam
WWW (department): http://www.nd.edu/~soc
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