Great summation of the issue! ZIP code related issues are a constant problem. Often the administrators of data sets don't know how to geocode a full address, an

Great summation of the issue! ZIP code related issues are a constant problem. Often the administrators of data sets don't know how to geocode a full address, and there are few easy ways to have participants record 'good' geographies. Can you imagine asking people whether they know what Census Block they live in? So we end up with a lot of data sets where ZIP codes become bad short-hand for geography. Last year I worked on a study where the geographic data had been fuzzed prior to passing it along to the study team, a process that unfortunately resulted in the patient addresses being simplified to just the ZIP code provided by the patient. There were two major issues beyond the general unsuitability of ZIP codes as geography: first, ZIP codes don't seem to be verified during the course of patient care. They are recorded (incorrectly at a minimum rate of ~0.2%) as a part of a patient address during the creation of the initial record. Even if the address is used for mailings, a bad ZIP does not result in mis-delivered mail in the vast majority of cases due to the availability of city, state, and street address data in the full address. The issue is just never discovered until you are put into the position of relying on only the ZIP code for geography, at which point the mitigating data (the full address) is unavailable. Second, even when ZIP codes do match to Census ZCTAs (the closest thing to 'ZIP code geographies' available and commonly utilized) there are some ZIP codes that do not have exactly matching ZCTAs. For example, 03911 and 04565 are real ZIP codes without (exact) matching ZCTAs. It would be preferable if address data, before being obfuscated for data anonymity reasons, was properly geocoded. After geocoding, the resulting geography could then be fuzzed for anonymity. Of course, this would just lead to arguments about what constitutes proper diligence in geocoding :)