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From |
Maarten buis <maartenbuis@yahoo.co.uk> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: AW: st: RE: RE: estimation with a time trend. |

Date |
Mon, 5 Jul 2010 12:43:07 +0000 (GMT) |

--- On Mon, 5/7/10, Martin Weiss wrote: > Then I do not understand the word "midpoint". I thought you > meant something like the mean or median? You want the value 0 to represent some meaningful point in time. Most important is that it lies within the range of your data. Which point you choose after that is more a matter of convenience: If you choose the minimum then your baseline represents the begining of your observed period, which is sometimes helpful when writing up your results. ("In the begining we found XXX, and as time progressed ...") It is often nicer to think in "nice round numbers" (e.g. multiples of 10), so you can move this baseline a bit to the right by choosing "the next round number" (e.g. choose 1910 instead of 1907). Data often tends to be sparse at the extreme ends of time, so the minimum does represent a number within the observed period, but the information about this period is often still very sparse. Choosing some central value (mean, median), can for that reason help the stability of some estimates in complex models. You might be interested in one specific point in time, in which case it makes sense to declare that point as 0. -- Maarten -------------------------- Maarten L. Buis Institut fuer Soziologie Universitaet Tuebingen Wilhelmstrasse 36 72074 Tuebingen Germany http://www.maartenbuis.nl -------------------------- * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**AW: st: RE: RE: estimation with a time trend.***From:*"Martin Weiss" <martin.weiss1@gmx.de>

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