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Re: st: Graphs With Log Scale: A Bug?


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Graphs With Log Scale: A Bug?
Date   Wed, 28 May 2008 11:24:56 +0100 (BST)

--- "Vladimir V. Dashkeyev" <dashkeyev@iet.ru> wrote:
> I drew a two-way plot with a linear prediction line -lfitci- of X on
> natural logarithm of Y. Next, I drew the plot of X on Y with log
> scale option -yscale(log)-.
> 
> To my surprise regression line changed its slope. The slope is
> greater with the -yscale(log)- option. I used the same X axis and
> the second Y-axis for the linear prediction graph .
> Is this a bug or am I doing something wrong?

This is not a bug: in the first scenario you are thinking that there is
a linear relationship between ln(Y) and X and you are showing the
predictions, while in the second scenario you are thingking that there
is a linear relationship between Y and X and then transforme the
predictions to a log scale. So the results are different because the
models are different.

-- Maarten


-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------


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