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

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

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

Date |
Mon, 5 Jul 2010 15:41:19 +0100 |

Good question, but clearly 1. Most postings in the thread, and the specific suggestions you received, were sent _before_ you made it clear that you were using -xtreg-. 2. If the question is, how best to estimate a time trend, with nothing else said, then translating time to a sensible origin remains good general advice. Nick n.j.cox@durham.ac.uk natasha agarwal On Mon, Jul 5, 2010 at 2:22 PM, Martin Weiss <martin.weiss1@gmx.de> wrote: > > <> > > The coeff for "t" will stay the same, then, no matter how you "center" it: > > ************* > use http://www.stata-press.com/data/r11/nlswork, clear > egen t=group(year) > xtreg ln_wage wks_work tenure south nev_mar age t, fe vce(robust) > replace t=t-7 > xtreg ln_wage wks_work tenure south nev_mar age t, fe vce(robust) > replace t=t-3 > xtreg ln_wage wks_work tenure south nev_mar age t, fe vce(robust) > ************* I tried this and as you said the coefficient stays the same. I was wondering then what is the point in doing this then? natasha agarwal > > On Mon, Jul 5, 2010 at 2:01 PM, Nick Cox <n.j.cox@durham.ac.uk> wrote: >> Your original question was >> >> "I was trying to estimate a production function with an unbalanced >> firm-year panel data and wanted to include a time trend. However I was >> not sure if the time trend was created correctly. >> >> egen t=group(year) >> >> I was wondering if anyone could please tell me if this was correct?" >> >> Who knows whether the commands you are using "mean center" the data if >> you do not tell us what they are? > > I am sorry about this. > > I issue the following line of commands: > > egen t=group(year) > xtreg lnrval lnk lnw lnvfdi t, fe vce(robust) >> natasha agarwal >> >> On Mon, Jul 5, 2010 at 1:14 PM, Maarten buis <maartenbuis@yahoo.co.uk> >> wrote: >> >>> --- On Mon, 5/7/10, natasha agarwal wrote: >>>> I am afraid I did not understand "year- (or -year- >>>> MINUS> midpoint) for interpretability?" >>> >>> Say you have a variable representing year of birth >>> ranging between 1910 and 1980. I would then usually >>> have a line like this in my do-file: >>> >>> gen c_year = year - 1910 >>> >>> Afterwards I would use c_year instead of year. In >>> this case "midpoint" is 1910, and makes sure that >>> your new variable is shifted to the left such that >>> it has the value zero in 1910. This makes sure >>> that the baseline in your models refer to a point >>> at the beginning of your observed period. This is >>> particularly important if you include interactions >>> or if you care about the constant (e.g. in a random >>> effects model) >> >> I am estimating the model with a within estimator. I thought that they >> mean center the data anyways? * * 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**:**Re: st: RE: RE: estimation with a time trend.***From:*Maarten buis <maartenbuis@yahoo.co.uk>

**Re: st: RE: RE: estimation with a time trend.***From:*natasha agarwal <agarwana2@googlemail.com>

**RE: st: RE: RE: estimation with a time trend.***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**Re: st: RE: RE: estimation with a time trend.***From:*natasha agarwal <agarwana2@googlemail.com>

**Re: st: RE: RE: estimation with a time trend.***From:*natasha agarwal <agarwana2@googlemail.com>

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