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st: Re: linear vs log-linear regression: specification test

From   "Scott Merryman" <[email protected]>
To   <[email protected]>
Subject   st: Re: linear vs log-linear regression: specification test
Date   Tue, 28 Oct 2003 23:32:19 -0600

----- Original Message ----- 
From: <[email protected]>
To: <[email protected]>
Sent: Tuesday, October 28, 2003 8:28 PM
Subject: st: linear vs log-linear regression: specification test

> Finally, what role should mechanistic theory/plausibility/functional
> relationship (if available)  play in deciding which
> mathematical/regression  relationship should be used (my feeling is a
> major one)?     Drawing in part from an example in the Stata manual :
> if I were trying to establish  on a relationship between, say, auto fuel
> consumption in gallons per mile and weight, I would probably decide to
> use a direct linear relationship based on the physics  and my underlying
> notions of what the relationship between energy requirements  and mass
> moved  regardless of how good a logged gallons per mile vs. weight  plot
> looked or how much better its R2 value might be.  To me, taking a log of
> the gallons per mile and regressing this on the weight of the automobile
> would imply a vastly different mathematical relationship between the
> dependent and independent variables.

The semi-log form may provide coefficients that have a very useful
interpretation.  In this case, each unit change in weight would change mpg in
percentage terms.


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