Our data warehouse doesn't deal with MSIS -- we have been using MAX data as produced by Mathematica since it started being available -- so I don't have a lot of ready info off the top of my head. However, I did find a reference to this in some of our QA documentation: http://www.cms.gov/Research-Statistics-Data-and-Systems/Computer-Data-and-Systems/MSIS/downloads/msisdd2010.pdf It might give you a start on the claims and eligibility files. Provider files that have not been through the MAX process are state-specific and I don't really know anything about them; I would think the best course would be to approach the source of the files for whatever info they might have. TelligenOne is right -- for MSIS you need to talk to the people who are responsible for preparing the data for transmission to HHS. I sympathize because I know it's often difficult to locate the right person to talk to but once you find him or her they will steer you straight a lot faster than any of us will.
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