This variable is the unique plan benefit package (PBP) number for the plan sponsor's contract. CMS assigns an identifier to each PBP within a contract that a plan sponsor has with CMS. This was the Plan ID for the plan in 2016 (the reference year). It may or may not be the same as the Plan ID in the prior year (2015).
This field is a key that links the plan sponsor's contract and plan identifiers.
All Contract and Plan ID that were active in 2016 appear in this data file. To determine whether the Contract and Plan IDs in the data file for the reference year (year of the data file) represent the same plan in the prior year, compare this variable (along with the corresponding CONTRACT_ID_16) to the PLAN_ID_15 (and CONTRACT_ID_15).
You need to know both the contract number (variable called CONTRACT_ID_YY) and plan benefit package identifier in order to identify the specific plan benefit package offered to beneficiaries.
The CCW constructs the Plan Characteristics File from information submitted by plan sponsors to CMS’s Health Plan Management System (HPMS).
Source: CMS (HPMS Files)