> -----Original Message-----
> From: [email protected] [mailto:owner-
> [email protected]] On Behalf Of [email protected]
> Sent: Thursday, October 06, 2005 6:46 PM
> To: [email protected]
> Subject: st: RE: RE: interaction
>
> In the interaction model, when group=1 the equation is
> ln(y)=constant+ b2 + (b1 + b3)*time.
>
> Then the effect of group is (exp(b1+b3)-1)*100. which turns out to be 2.6
> percent.
Is this correct?
If the model is:
ln(y)= constant + b1*(time) + b2*(group) + b3*(group*time)
Then would not the percent change for a unit change in group be:
Y1/Y0 - 1 = (exp{b0 + b1*T + b2*1 + b3*1*T} / exp{b0 + b1*T}) - 1
= (exp{b0}exp(b1*T}exp(b2}exp{b3*T} / exp(b0}exp(b1T}) - 1
= (exp(b2}exp{b3*T}) - 1
= exp{b2 + b3*T} - 1
Scott
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