Re: how to determine the variance of dependant variable when all the var. of ind. variables r known in a linear relation
- From: Bruce Weaver <bweaver@xxxxxxxxxxxx>
- Date: Thu, 16 Nov 2006 18:06:20 -0500
Old Mac User wrote:
Greg...
I think it would be nice if you would give this person the answer
without asking him/her to dig further into VAR(y) = E{ (y - E{y} )^2
}
IMHO, when a person comes to this board with a reasonable question...
expresses that question in "plain English"... then we should provide a
direct and practical answer without asking them to "learn all about
statistics".
Tutoring students who are attending courses for credit is one thing.
Helping someone with a simple question is another. As a consultant I'm
expected to "answer questions", not drive my clients to dig into
matters of little or no concern to them.
Full Disclosure: I'm a chemical engineer and also a statistician.
Something like...
Var(y) = (a^2) *Var(X1) + (b^2) * Var(X2)
assuming that a, b, and c are constants which are not subject to random
variation
and assuming that the errors in X1 and X2 are not correlated with each
other.
OMU
And if they are correlated, I believe it would be:
Var(y) = (a^2) * Var(X1) + (b^2) * Var(X2) + 2ab*COV(X1,X2)
Have I got that right?
--
Bruce Weaver
bweaver@xxxxxxxxxxxx
www.angelfire.com/wv/bwhomedir
.
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