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Re: st: Changing spells to person-years


From   David Kantor <kantor.d@att.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Changing spells to person-years
Date   Mon, 20 Nov 2006 13:59:36 -0500

At 01:30 PM 11/20/2006, Justin wrote:
Hello trusty listservers,


I have spell that that I want to convert into a long file. Using a life history calendar, I have below four people who show changing residences (rural/urban) across their life course. Each row represents one person. For instance, person 1 lived in a rural area from 0-3, an urban area from 4-6, rural from 7-15, and urban 16-20. That person at the time of the survey was 20 years old. Person 3 lived in a rural area her whole life.


cw2i1 cw2i1s cw2i1e cw2i2 cw2i2s cw2i2e cw2i3 cw2i3s cw2i3e cw2i4 cw2i4s cw2i4e

rural 0 3 urban 4 6 rural 7 15 urban 16 20

urban 0 30 rural 31 32 . . . . . .

rural 0 38 . . . . . . . . .

urban 0 17 rural 18 54 urban 55 57 . . .


While I have shown how it looks for residence location, the same exists for education and other variables. I know I could generate hundreds and hundreds of new variables so that each cell in the calendar represents a variable in STATA, but from reading the listserv, it seems that there is an easier way, although it is not clear to me. How can I turn this into a person-year file?

This is somewhat straightforward for this one attribute. It's a -stack- or -reshape long- matter.

BUT, what happens when you combine other attributes. Do they all fit into the same patterns of years? Or does each attribute have its own pattern of years?

If the latter, then you may need to first treat each attribute separately. Then put them together with a -merge-.

Another matter: Is it always true that the end of a spell is start_of_next_spell -1 ? (No gaps, no overlaps.) If so, then you can eliminate the end dates. (Though, you may need to insert a dummy spell for each person to signify the end of the latest-known spell.) And then, later, in the -merge- step, the match-key variables will be person-id and start_year. (But in any case, you should not include the end_dates in the merge.)

Under this scheme, the result will be that for each person, different attributes will all share the same pattern of spells, using a "fine" granulation of years -- where the start dates are the union of all start dates of the spells of the different attributes. Then, some attributes will not change at every spell transition. A spell transition will occur when at least one attribute changes.

If you spell out the structure of your data in more detail, then we can better help you.
HTH
--David

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