Do "Consumer-Directed" health plans bend the cost curve over time?

"Consumer-Directed" Health Plans (CDHPs), those with high deductibles and personal medical accounts, are intended to reduce health care spending through greater patient cost exposure. Prior research agrees that in the first year, CDHPs reduce spending. There is little research and in it results are mixed regarding the impact of CDHPs over the longer term. We add to this literature with an intent-to-treat, difference-in-differences analysis of health care spending over up to three years post CDHP offer among 13 million person-years of data from 54 large US firms, half of which offered CDHPs. To strengthen the identification, we balance observables over time within firm, by developing weights through a machine learning algorithm, generalized boosted regression. We find that spending is reduced for those in firms offering CDHPs in all three years post offer relative to firms continuing to offer lower-deductible plans. The reductions are driven by spending decreases in outpatient care and pharmaceuticals, with no evidence of increases in emergency department or inpatient care over the three-year window.