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From |
Ulrich Kohler <kohler@wz-berlin.de> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: dates |

Date |
Thu, 21 Aug 2003 15:16:58 +0200 |

Nick, Thank you very much. uli Nick Cox wrote: > Ulrich Kohler > > > I have two questions on elapsed dates: > > > > The mdy()-function returns the elapsed date, counting from > > January 1 1960. > > > > . display mdy(1,1,1960) > > 0 > > > > . display mdy(1,2,1960) > > 1 > > > > . display mdy(12,24,100) > > -678993 > > > > However > > > > . display mdy(12,24,99) > > > > returns a missing value, as does > > > > . display mdy(12,24,00) > > . > > > > What is the reason that mdy() returns missing with 2 digit > > years ( to prevent > > the user from using two digit years?) > > Dates in Stata start at 1 January 100. That once put paid > to a project I wanted to do on modelling of > daily temperature measurements and olive prices under > Julius Caesar, but Stata Corp were unyielding: they have > no interest in changing this limit. > > As you say, elsewhere you can indicate separately a two-digit > year and a century, so that "52" and "19" can be coupled > together. It gets a bit awkward to imagine "52" and "0" > being coupled together to indicate the year 52. > > > The second question is just for curiosity. Is there any > > reason for using the > > January 1 1960 as zero? It seems quite common in software > > programs, but why? > > Interesting little historical question. I guess some > data base or spreadsheet program started this as a > convention, and lots followed. Perhaps there was a > presumption that nobody much wanted to deal with > data before that. (Depending upon implementation, > perhaps you could have dates before as negative numbers, > as in Stata.) > > Also, suppose you used 1 January 1 as a basis. Then > most daily dates which would be used would be represented > by integers ~ 700,000 and that could tie up lots of bytes which, > a few years ago, was of course a much bigger deal. > > As far as Stata is concerned, a more natural base > would be 21 January 1952 (see [U] p.302), but that > would be rather too idiosyncratic to fit the bill. > > Nick > n.j.cox@durham.ac.uk > > > * > * 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/ -- kohler@wz-berlin.de * * 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: RE: dates***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

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