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From |
Mattia Landoni <mattia.landoni@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Re: Same code, same machine, same data, different results |

Date |
Thu, 6 Sep 2012 20:47:37 -0400 |

Thanks for the jokes and the constructive answers. There is no m:m merge, and the same variables are dropped each time. The problem was indeed one of sorting, as two of the answers mentioned, together with a wrong use of indexing. There was a command such as (simplifying) sort id year generate a_lag = a[_n - 1] if id == id[_n - 1] the dataset is quarterly, so it has more than one observation per year. Each time I ran the code, the dataset had a slightly different sorting and some rows were assigned each time different values. On Wed, Sep 5, 2012 at 5:10 PM, Mattia Landoni <mattia.landoni@gmail.com> wrote: > Dear statalisters, > > a friend of mine has a bizarre problem. She is running a regression as follows: > > xi: regress a b c i.d i.e > > and her output is different every time. Has anyone ever seen a > behavior like this? Below are some details. > > Environment: > - Stata 11 > - Windows 32-bit > > Precise description: > The do-file imports several files from .csv, then merges them, then > runs the regression. If I run the do-file, I get certain results. If I > issue the same regression command again, I get again the same results, > as it should be. However, if I re-run the do-file from the beginning, > I get slightly different results and the regression even reports a > slightly different number of observations. (Say, 2663 vs. 2666). Every > time all the data are taken afresh from the same static .csv sources. > There is nothing random about the do-file, that I know. The xi: > command generates about 200 i-variables and a few, maybe 10, are > dropped because of collinearity. There are more than 2500 > observations. > > I could post the do-file here, but it's big and messy. If anyone has > any insight after reading the above description, I'd be very glad to > hear it. > > Thanks, > > Mattia > > -- > Mattia Landoni > +1 217 4-A-QUANT (from US) > +39 02 3206 21676 (from Italy) > GMT -05:00 (US East) -- Mattia Landoni +1 217 4-A-QUANT (from US) +39 02 3206 21676 (from Italy) GMT -05:00 (US East) * * 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/

**Follow-Ups**:**Re: st: Re: Same code, same machine, same data, different results***From:*Nick Cox <njcoxstata@gmail.com>

**References**:**st: Same code, same machine, same data, different results***From:*Mattia Landoni <mattia.landoni@gmail.com>

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