He has conducted and led systematic reviews in a number of areas, including chronic pain and musculoskeletal conditions, screening and prevention, diagnostic testing, and prognosis. Many of his reviews have been used to develop clinical practice guidelines by the American College of Physicians, the US Preventive Services Task Force, the American Pain Society, the Centers for Disease Control and Prevention, and others. He has also conducted methodological research in the conduct of systematic reviews and has led or participated in a number of groups that developed standards for conducting research and systematic reviews. He has served as Director of the American Pain Society clinical guidelines program, a GRADE methodologist for several World Health Organization guidelines, is a member of the Cochrane Back Review Editorial Board, and co-chair of the National Quality Forum Musculoskeletal Standing Committee.

Areas of interest
Screening and prevention, including HIV, HBV, and HCV screening, prostate cancer and bladder screening, screening for diabetes, lipid screening, vision screening in children and older adults, oral health screening in children, screening for hearing impair