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notes The Third Child in Colombia

notes The Third Child in Colombia - Eco 572 Research...

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Eco 572: Research methods in Demography The Third Child in Colombia We will look at the interval from second to third birth using Colombian WFS data, circa 1976. We start from an extract that has the dates of R's birth, date of interview, the birth history, date of first union if any, and current and childhood type of place of residence. . use http://data.princeton.edu/eco572/datasets/cofertx, clear (COSR02 extract) Time at Risk and Event Indicator We will use intervals that start in the ten years before the interview and exclude twins. (The results are a bit different from my paper with Hobcraft, which used all birth intervals, but I can reproduce the earlier results by removing the period restriction.) . keep if b022 >= v007-120 & b022 < v007 (4144 observations deleted) . drop if b032==b022 // only 6 (6 observations deleted) We construct time at risk starting in the middle of the month of birth of the second child and ending in the middle of the month when the third child is born or at the end of the month before the interview, whichever occurs first . gen expo = b032 - b022 . replace expo = v007 - b022 -0.5 if v007 <= b032 (496 real changes made) . gen third = b032 < v007 If we stset the data we can take advantage of Stata's survival analysis facilities. For example it is very easy to obtain a plot a Kaplan-Meier estimate of survival at parity 2: . gen id=_n . stset expo, fail(third) id(id) id: id failure event: third != 0 & third < . obs. time interval: (expo[_n-1], expo] exit on or before: failure ------------------------------------------------------------------------------ 1228 total obs. 0 exclusions ------------------------------------------------------------------------------ http://data.princeton.edu/eco572/cobint.html (1 of 8) [2/12/2008 10:47:48 AM]
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Eco 572: Research methods in Demography 1228 obs. remaining, representing 1228 subjects 732 failures in single failure-per-subject data 34388 total analysis time at risk, at risk from t = 0 earliest observed entry t = 0 last observed exit t = 115.5 . sts graph failure _d: third analysis time _t: expo id: id . graph export co3rdkm.png, replace (file co3rdkm.png written in PNG format) Segments of Exposure We will take advantage of Stata's facilities to split the exposure into 3 month segments. The cutpoints have the form 0 3.5 6.5 9.5 ... 57.5 60.5 120. . stsplit segment, at(0 3.5(3)60.5 120) http://data.princeton.edu/eco572/cobint.html (2 of 8) [2/12/2008 10:47:48 AM]
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Eco 572: Research methods in Demography (9844 observations (episodes) created) Stata's built-in variables _t and _t0 have the start and end of each segment and _d has the 'death' indicator. We use these to compute events and exposure. This is not a bad time to save the data.
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