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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

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

Date |
Thu, 29 May 2008 14:38:36 +0100 |

Glad the advice was helpful. Nick Vladimir V. Dashkeyev Nick, I understand that "make it work for me" approach is not acceptable. But before asking I made several attempts and failed. I do appreciate your help, I managed to get what I wanted thanks to your advice. Thank you again, Vladimir On Wed, May 28, 2008 at 5:48 PM, Nick Cox <n.j.cox@durham.ac.uk> wrote: > Please accept more responsibility for solving problems. > > It is just a matter of (a) reading the help and (b) applying textbook formulae. > > Here is a sketch: > > local level = <your_choice, e.g. 95> > regress <whatever> > tempvar pred se ul ll > predict `pred' > predict `se', stdp > local level = (100 - `level') / 200 > gen `ul' = `pred' + invttail(e(df_r), `level') * `se' > gen `ll' = `pred' - invttail(e(df_r), `level') * `se' > > Nick > n.j.cox@durham.ac.uk > > Vladimir V. Dashkeyev > > Nick, > > Thanks for the answer. I did not use -predict- since this approach > does not provide a quick way for drawing confidence intervals. If I'm > wrong and there is a way to draw CI, please, let me know about it. > > Thank you, > Vladimir > > On Wed, May 28, 2008 at 4:21 PM, Nick Cox <n.j.cox@durham.ac.uk> wrote: >> My advice is to use -predict- after each model fitted to save the results in separate variables. Then draw one graph to get you want. I wouldn't approach this via -lfit- or >> -lfitci-. That will also oblige you to make explicit what you are doing. >> >> Nick >> >> Vladimir V. Dashkeyev >> >> 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? >> >> Maarten buis >> >>> --- "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. * * 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/

**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>

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

**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>

**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>

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