Project Summary Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of death in the United States, and HMG- CoA reductase inhibitors (statins) are the most effective pharmacotherapy for reducing the risk of ASCVD. Nearly half of U.S. adults could benefit from taking a statin. Yet even among those at the highest risk of ASCVD, many are never offered them by their physician, and half of those who start discontinue statins within one year. Shared decision making (SDM) helps patients make informed decisions based on their individualized predicted benefits and harms of different treatment strategies. Decision aids (DAs) are tools that facilitate SDM. Statin Choice is an electronic health record (EHR)-embedded DA designed to be used by physicians to facilitate SDM with patients for statin therapy. Statin Choice is available free of charge in Epic, the most commonly used EHR platform in the U.S. In small trial settings, use of Statin Choice was moderately associated with primary and secondary statin adherence. Yet these studies had a number of important limitations such that the impact of Statin Choice on adherence remains unknown. In 2015 the Cleveland Clinic Health System enabled Statin Choice as an option in the EHR for physicians to use when discussing statins with patients. We found patients who viewed Statin Choice during a primary care visit had three times higher odds of leaving the visit with a statin prescriptions compared to those who did not. As this is the necessary first step on the pathway to adherence, Statin Choice may represent a powerful and scalable tool to improve statin adherence. Our overall goal is to improve statin adherence through expanded use of Statin Choice, particularly among patients at highest risk for ASCVD events. In Aim 1 we will conduct an observational study on over 180,000 primary care patients and 700 physicians to describe physician variation in use of Statin Choice by patient factors, including race/ethnicity and socioeconomic position, and assess the impact of Statin Choice exposure on primary and secondary adherence. Decision aids can only be useful if physicians use them. We will use real world physician variation in use of Statin Choice to sample physicians to participate in semi- structured interviews about their experiences using the tool. Aim 1 will generate important new information on use of Statin Choice under real world conditions. In Aim 2 we will conduct a cluster randomized controlled trial of clinical decision support for Statin Choice on primary and secondary adherence. Our randomized trial design will allow us to establish causality and determine whether expanded use of Statin Choice can have a meaningful impact on statin adherence. Numerous health systems have integrated Statin Choice in their EHR, yet far more could do so. Our study in a major health system will generate two crucial pieces of knowledge to support this effort: 1) we will determine the true impact of Statin Choic...