Practical example of the care you must apply when analysing data by zip code.
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. Dr. Tony Grubesic, an Arizona State University professor, has called them "one of the quirkier 'geographies' in the world." Dr. Nancy Krieger, a Harvard University professor, and colleagues have called out their unacceptability for small-area analyses.
http://phys.org/news/2016-09-codes-masked-problem-flint.html
