Medicare accountable care organizations are associated with modest reductions in spending and use of hospitals and emergency departments, according to a study published this week by JAMA Internal Medicine. The study compared changes in spending and usage for beneficiaries cared for by ACO physicians and non-ACO physicians between January 2009 and December 2013, including a subgroup of clinically vulnerable beneficiaries. After ACO contract implementation, quarterly spending per beneficiary decreased by $34 in the study’s overall Medicare population and $114 in the clinically vulnerable population, which included patients with conditions such as diabetes, coronary artery disease and congestive heart failure.