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From |
Julia Gamas <jgamas@MIT.EDU> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Merge chaniging census tracts |

Date |
Thu, 5 May 2005 12:55:06 -0400 |

Hi all, I have to merge two databases from two different years where each observation is a census tract. The challenge is avoiding double counting after the merge, as a result of census tracts changing through time. I would like to create a code that identifies the groups of tracts that split up or merged but am not sure how to do it. Other than doing it by hand (I have 4000 tracts), I'm wondering if there is a somewhat automatic way to do this in Stata. Currently, if I were to merge the two datasets using the corresponding equivalence table I would get something like this. year 1 year 2 Code pop code pop what happened to tract over time: xx 22 lm 10 census tract from year 1 split into two xx 22 pq 5 " pl 12 pl 5 census tract remained but got bigger because da 5 pl 5 census tracts from year 1 merged into an existing gr 1 pl 5 tract fa 8 fa 16 census tract remained the same 00 0 no 10 census tract did not exist in year 1 but appeared in year 2 00 0 lp 8 " ll 10 00 0 census tract existed in year 1 but disappeared in year 2 pp 10 00 0 " If at this point I were to collapse (sum) the population for year 2, for example, then I would end up triple counting population in census tract pl, similarly, if I were to collapse (sum) population for year 1. Population for pl in year 2 would be counted as 15 when it is only 5. Population for tract xx would be counted as 44 when it is only 22. As an intermediate step I was thinking of doing the following: year 1 year 2 newcode Code pop code pop 1 xx 22 lm 10 1 xx 22 pq 5 2 pl 12 pl 5 2 da 5 pl 5 2 gr 1 pl 5 3 fa 8 fa 16 4 00 0 no 10 5 00 0 lp 8 6 ll 10 00 0 7 pp 10 00 0 That way, I could keep track of the population for each tract or "group" of tracts and end up with something like this: year 1 year 2 newcode pop pop 1 22 15 2 18 5 3 8 16 4 0 10 5 0 8 6 10 0 7 10 0 How do I tell stata how to generate newcode (i.e. can I get stata to recognize groups of census tracts with the same code and assign them a newcode, for both years)? Any help would be appreciated. Sincerely, Julia A. Gamas Mexico City Project MIT * * 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/

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