----- 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.
Scott
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