Emma--
I think this question is ill-formed or incomplete. There are various
methods of "standardizing" coefficients, and you can
view http://www.indiana.edu/~jslsoc/stata/spost9_ado/listcoef.hlp
to see several in Stata.
But if you want to "standardize" a linear combination of coefficients
(not an interaction term, to be sure, but also not bX + CX^2, I am
guessing), you will need to add some specificity.
Let us suppose you want to "standardize" the marginal effect of X, given by
b + 2cX
(the partial of your bX + CX^2) in some model. Do you mean to divide
that combination by the estimated standard deviation of X to interpret
the marginal effect in standard deviation units? At what value of X?
Hard to see exactly what you actually want here, but it may be
-lincom-.
sysuse auto, clear
g mpg2=mpg^2
reg pr mpg*
su mpg if e(sample)
local m=r(mean)
local s=r(sd)
lincom (_b[mpg]+2*_b[mpg2]*`m')/`s'
On 3/1/07, emmmasa <emmmasa@yahoo.com> wrote:

Dear all:
Could anyone advise how to derive the overall beta
(standardized) coefficient for an interaction term
(e.g., bX + CX^2) for a standard OLS regression?
Thanks very much.
Emma

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