Some have proposed an "excise tax" for high cost 'Cadillac' insurance plans. A study published in Health Affairs in December 2009 found that high-cost health plans do not provide unusually rich benefits to enrollees. The researchers found that only 3.7% of the variation in the cost of family coverage in employer-sponsored health plans is attributable to differences in the actuarial value of benefits. Only 6.1% of the variation is attributable to the combination of benefit design and plan type (e.g., PPO, HMO, etc.). The employer's industry and regional variations in health care cost explain part of the variation, but most is unexplained. The researchers conclude ". . . that analysts should not equate high-cost plans with Cadillac plans, . . . [w]ithout appropriate adjustments, a simple cap may exacerbate rather than ameliorate current inequities"
