A health care service plan that issues, sells, renews, or offers health care service plan contracts for health care coverage in this state, including a grandfathered health plan, but not including specialized health care service plan contracts that provide only dental or vision services, shall provide an annual rebate to each enrollee under that coverage, on a pro rata basis, if the ratio of the amount of premium revenue expended by the health care service plan on the costs for reimbursement for clinical services provided to enrollees under that coverage and for activities that improve health care quality to the total amount of premium revenue.