What is the Common Working File?

The term Common Working File (CWF) is about as old as any IT terminology in our industry.  I have used it myself since we began the company in 1986.  Despite our common understanding of this concept, I have to admit that I was not really sure what it was, where it was stored, or how it was maintained.  I decided to do a little research. Here are the results.

The CWF is specific to Medicare.  It is a collection of records maintained on behalf of each Medicare beneficiary that covers these four general areas of information:

Entitlement data

Utilization History

Medicare Secondary Payer (MSP)

Health Maintenance Organization (HMO)

This information is stored in a separate record for each beneficiary for each of these data categories.

Although we think of the CWF as a single database, it is actually comprised of 9 databases called Hosts.  Each beneficiary is assigned to only one host.  This is determined by where the person signs up for their SSA benefits.  Here are the host sites and the states that are assigned to each: 
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