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From |
"Vladimir V. Dashkeyev" <dashkeyev@iet.ru> |

To |
statalist@hsphsun2.harvard.edu |

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

Date |
Wed, 28 May 2008 15:45:42 +0400 |

Martin, Thanks for the reply. I should have emphasized in the first message, that I run -lfitci- of X on ln(Y) in both scenarios. The difference is in the scatter plot. In the first scenario I use ln(Y), and in the second -- Y with log scale option. I expected to get the same linear prediction line and the same scatter plot. But after I posted that question, I compared the graphs once again and realized that the real problem is with the Y axis scale. If I draw a scatter and prediction line on the same Y axis, everything is fine. Yet if I draw the same scatter with 2 Y axes I get different range of values on Y1 and Y2 axes. I need two Y axes for overlaid drawing of the scatter with -yscale (log)- option and linear prediction of X-ln(Y). Setting range on both axes to the same values did not help. They are very close but still shifted a bit. So the arrangement of observations and prediction line is not correct. So it's not a bug, but still a problem I have to solve. Is there any way to "tie" axis Y1 with axis Y2? Thanks, Vladimir On Wed, May 28, 2008 at 2:24 PM, Maarten buis <maartenbuis@yahoo.co.uk> wrote: > --- "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/ > ----------------------------------------- > > > __________________________________________________________ > Sent from Yahoo! Mail. > A Smarter Email http://uk.docs.yahoo.com/nowyoucan.html > * > * For searches and help try: > * http://www.stata.com/support/faqs/res/findit.html > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**RE: st: Graphs With Log Scale: A Bug?***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**Re: st: Graphs With Log Scale: A Bug?***From:*"Vladimir V. Dashkeyev" <dashkeyev@iet.ru>

**References**:**st: Graphs With Log Scale: A Bug?***From:*"Vladimir V. Dashkeyev" <dashkeyev@iet.ru>

**Re: st: Graphs With Log Scale: A Bug?***From:*Maarten buis <maartenbuis@yahoo.co.uk>

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