Medicare Part D formulary tier identifier. This field represents the cost sharing tier in which the product was placed in the sponsor's formulary.
This identifier is also a key that links a Part D sponsor's cost sharing tier record to a prescription drug event record via contract ID, plan ID, and tier ID.
Up to six tiers are possible.
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)