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posted by martyb on Wednesday September 21 2016, @02:29PM   Printer-friendly
from the carefully-choose-your-buckets dept.

My job was to examine blood lead data from our local Hurley Children's Hospital in Flint for spatial patterns, or neighborhood-level clusters of elevated levels, so we could quash the doubts of state officials and confirm our concerns. Unbeknownst to me, this research project would ultimately help blow the lid off the water crisis, vindicating months of activism and outcry by dedicated Flint residents.

As I ran the addresses through a precise parcel-level geocoding process and visually inspected individual blood lead levels, I was immediately struck by the disparity in the spatial pattern. It was obvious Flint children had become far more likely than out-county children to experience elevated blood lead when compared to two years prior.

How had the state so blatantly and callously disregarded such information? To me – a geographer trained extensively in geographic information science, or computer mapping – the answer was obvious upon hearing their unit of analysis: the ZIP code.

Their ZIP code data included people who appeared to live in Flint and receive Flint water but actually didn't, making the data much less accurate than it appeared.

ZIP codes – the bane of my existence as a geographer. They confused my childhood friends into believing they lived in an entirely different city. They add cachet to parts of our communities (think 90210) while generating skepticism toward others relegated to less sexy ZIP codes.

A tale to remind the scientists and technologists among us why it's important to do our jobs well.


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  • (Score: 3, Informative) by DeathMonkey on Wednesday September 21 2016, @05:25PM

    by DeathMonkey (1380) on Wednesday September 21 2016, @05:25PM (#404851) Journal

    Yes, they should be using the proper tool for the job which is the The Public Land Survey System (PLSS) [nationalmap.gov]
     
    This is very standard practice so I'm not sure why they were using zipcodes in the first place.

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  • (Score: 4, Insightful) by HiThere on Wednesday September 21 2016, @06:24PM

    by HiThere (866) Subscriber Badge on Wednesday September 21 2016, @06:24PM (#404872) Journal

    Zip codes are easy to get. Few people know, e.g., their census tract, much less their block-face. Water bills are sent out by zip code. Electric bills are sent out by zip code. Etc. Everyone knows their zip code. All the records include the zip code.

    A couple of decades or so ago I was involved with processing data collected during the 1960 and the 1980 censuses. They'd redrawn a bunch of the census tract boundaries in the interim, splitting a few, consolidating a couple. Etc. The only data source that had sufficient detail to reconcile the two data sets were the individual addresses, which were not available. So we did the best we could with 1960 census tracts and 1980 block faces....but much of the data wasn't available at the block-face level of detail, so we had to estimate a proportional correction. UGH! Not good. But zip codes split both the 1980 and the 1960 census tracts in different ways. (I don't believe they split any block-faces, however...but city boundaries did.)

    There are lots of different geographical units, and each is designed for a particular purpose. (Census tracts, e.g., play a part in Gerymandering, but they're supposed to contain "about" the same number of people. They don't always, but commercial areas tend to have larger census tracts, and rezoning will affect what happens the next time census boundaries are redrawn.) When you use a unit for a purpose that it isn't designed for, you should expect problems. For some reason people rarely do.

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