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From |
David Kantor <dkantor@jhu.edu> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: nested loops for calculating a population 'at risk' |

Date |
Mon, 20 Sep 2004 14:14:45 -0400 |

At 06:37 PM 9/20/2004 +0100, Sue Lee wrote:

If I understand correctly -- that the bounds 167 and 259 apply to 02jan1988, and 168 and 260 apply to 02jan1988, and so on, then try this: (I'm not sure if this is right, since this will lead to absurdly long gestation limits. But then you just get nobody at-risk after some point.)Many thanks to those kind souls who responded to my initial query... i think perhaps i was not clear enough about what i am trying to do... so i'll try explaining again! the dataset contains a record for each baby born on each day from 1988 to 2000. we have a variable for birthdate and a variable for gestation at birth in days (dgest). i am interested in how to generate the following algorithm into workable STATA code: 1. for each date from 1 jan 1988 to 31 dec 2000 2. calculate the number of records that have dgest > 167 and < 259 on the current day (these are the 'cases at risk') 3. move forward a day 4. increase both dgest values by 1 and repeat step 2 (i.e., calculate the number of records on this day that have dgest > 168 and <260... these are the cases that were 'at risk' the day before) 5. move forward a day 6. repeat step 4 and 5 until max dgest value reached 7. sum the number of records 'at risk' for each day i'd be most grateful for any help or suggestions received!

gen int dgestmin = birthdate - d(01jan1988) + 167

gen int dgestmax = dgestmin + 92

gen byte atrisk = dgest > dgestmin & dgest < dgestmax

bysort birthdata: egen long numatrisk = sum(atrisk)

You can then reduce to one record per birthdate. Alternatively, the instead of the -egen-,

you can -collapse-, taking the sum of atrisk.

I hope this helps.

--David

David Kantor

Institute for Policy Studies

Johns Hopkins University

dkantor@jhu.edu

410-516-5404

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**References**:**st: RE: nested loops for calculating a population 'at risk'***From:*"Sue Lee" <Sue.Lee@lshtm.ac.uk>

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