Hello Lady or Sir,

I want to do model selection with 'step' function. But there is a trouble to
me.

For example, there are 5 independent variables, X0,X1,X2,X3 and X4; and 1
dependent variable y.
I want to run stepwise regression y ~ X0 + X1 + X2 + X3 + X4, and I want to
keep X0 always in the
model. Every time when I run command 'step' with 'keep', error information
"could not find function 'keep' "
is always shown.  Could you tell me how to use the parameter 'keep' in
'step' function?

Thank you very much and best regards,

Wenxin Liu
2009.11.02
-------------------------------------------------------------------------------------
Wenxin Liu, Postdoc., Scientific staff
State Plant Breeding Institute(720)
University of Hohenheim
70593 Stuttgart, Germany

PhoneNo.: +49-(0)711-459-22670
Telefax    : +49-(0)711-459-23841
Email       : wenxin.liu@uni-hohenheim.de  (academic)
        or     lwx.biostat@gmail.com             (personal)

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