Without the rebate pass-through requirement, the average increase would have been 18.2%.

The impact of the rebate pass-through requirement on each issuer's rate increase ranged from a minimum of 39.7% at one company to a maximum of 63.9%.

Related: Drug rebates under scrutiny: how prepared is your health plan?

In the large-group market, the rebate pass-through requirement led to average rate savings of 16.7% for the three rate change request filers, with a range of 0% to 33.2%.

PBMs: Pharmacy benefit managers help health insurers, self-insured employer health plans and other "payers" manage prescription drug benefits. PBMs often try to save customers money by negotiating "rebates," or arrangements for getting some of the cash spent on drug purchases back, with drug manufacturers or drug distributors.

One question has been whether PBMs have acted like stores that set "normal" clothes prices 50% too high so that they can always advertise a 30% off sale.

Mark Cuban and other PBM watchers have accused the big PBMs of pushing up the full list prices of drugs, in an effort to exaggerate the size of the savings they obtain for customers, and of finding ways to keep a high percentage of the rebates and other discounts that they do negotiate.

Defenders of the big PBMs have suggested that the critics are attacking the big PBMs because of anger at the PBMs' success at squeezing costs out of the prescription drug distribution system.

West Virginia's rebate pass-through requirement: The state's Pharmacy Audit Integrity Act, the statute that creates the rebate pass-through requirement, was signed into law in 2021 and took effect in 2022.

Insurers had to report on the impact of the rebate pass-through requirement on their rates starting with rate change requests filed in 2023 for 2024 coverage.

West Virginia defines a "small employer" as an organization with 2 to 50 employees. A large employer has 51 or more employees.

The first year: The new West Virginia pass-through requirement impact report shows that the effects of the requirement were similar in the first year and the second year.

In the first year the reporting requirement was in effect, the requirement cut the average rate increase at the five small-group coverage issuers by an average of 9.4 percentage points, or 49.4% of what the issuers say the average change would have been without help from the requirement, to 9.4%.

For the two issuers in the large-group market, the rebate pass-through requirement cut the average increase by 5.6 percentage points, or 37.2%. The rebate law helped one issuer lower its overall increase to 7.9%, from 9.6%, and the other to lower its overall increase to 10.7%, from 16.2%.

What it means: The new West Virginia figures appear to support the arguments of Mark Cuban and other PBM critics.

But the West Virginia report is based on data compiled by the issuers that filed the rate change requests, and the report provides no details about how the insurers computed the rebate requirement impact figures. The insurers' impact figures may give a misleading picture of the effects of the rebate requirement on small-group premiums.