Competing interests: The BMJ has judged that there are no disqualifying financial ties to commercial companies. The authors declare the following other interests: JAL is supported by a contract from the Agency for Healthcare Research and Quality (HHSP233201500020I), and is also supported by grants from the National Institute on Ageing (R21AG057400, R21AG057396, R33AG057383), National Institute on Drug Abuse (R33AG057395), and the Agency for Healthcare Research and Quality (R01HS026506), the Peterson Center on Healthcare. The BMJ policy on financial interests is here: https://www.bmj.com/sites/default/files/attachments/resources/2016/03/16-current-bmj-education-coi-form.pdf.