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From |
ncdcta00@uniroma2.it |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: expand and duration model |

Date |
Mon, 18 Feb 2008 08:46:36 +0100 |

Thanks a lot Nick, it work perfect. Catia Quoting n j cox <n.j.cox@durham.ac.uk>:

This is not the problem tackled by -expand-. Nor does -expandby- (a user-written program from SSC) claim to tackle anything like this problem. The problem has presumably been solved before, but off-hand I can't remember any program that does it. However, a few lines should get you most of the way. expand 2 sort id datealt by id: replace datealt = datebax[_n - 1] + 1 if mod(_n, 2) == 0 by id: replace datebax = datealt[_n + 1] - 1 if mod(_n, 2) == 0 by id: replace y = 0 if mod(_n, 2) == 0 by id: replace x = 0 if mod(_n, 2) == 0 by id: drop if _n == _N Consider -id- 1. 1 11/02/2001 14/08/2003 100 205 1 02/03/2005 05/06/2005 120 130 1 13/08/2005 18/12/2005 100 130 We -expand 2- and then -sort- to get this: _n 1 11/02/2001 14/08/2003 100 205 1 1 11/02/2001 14/08/2003 100 205 2 1 02/03/2005 05/06/2005 120 130 3 1 02/03/2005 05/06/2005 120 130 4 1 13/08/2005 18/12/2005 100 130 5 1 13/08/2005 18/12/2005 100 130 6 We need to work on the even-numbered observations, those with _n of 2, 4, ... -- which are identified by -mod(_n, 2) == 0-. We look backwards for the start date of each gap, and add 1; and forwards for the end of each gap, and subtract 1. A correction is that the last observation for each -id- will contain no useful information, so we -drop- it. On the other hand, you might know that your study ended at some time. Suppose your study ended on 31/12/2007. Then instead of by id: drop if _n == _N you should have by id : replace datebax = mdy(12,31,2007) if _n == _N You need to modify this if the recipe has to cope with gaps of length 0. Look for observations with -datebax < datealt- and -drop- them. I have not tested this code, but I hope it helps. Nick n.j.cox@durham.ac.uk Catia ===== I have a problem to understand how to expand my observation to stset my data to use in a duration model. I have the following data set: id datealt datebax y x 1 11/02/2001 14/08/2003 100 205 1 02/03/2005 05/06/2005 120 130 1 13/08/2005 18/12/2005 100 130 2.......... 2.......... so I want a dataset for the period that I don't observe the id: id datealt datebax y x 1 11/02/2001 14/08/2003 100 205 1 15/08/2003 01/032005 0 0 1 02/03/2005 05/06/2005 120 130 1 06/06/2005 12/082005 0 0 1 13/08/2005 18/12/2005 100 130 2......... 2....... 2.......... Someone can help me? I try with expandby but without results. * * 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/

Catia Nicodemo * * 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**:**Re: st: expand and duration model***From:*n j cox <n.j.cox@durham.ac.uk>

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