The Agency for Healthcare Research and Quality (AHRQ), through its Evidence-based Practice Centers (EPCs), sponsors the development of systematic reviews to assist public- and private-sector organizations in their efforts to improve the quality of healthcare in the United States. The Patient-Centered Outcomes Research Institute^® (PCORI^®) requested this report from the EPC Program at AHRQ. AHRQ assigned this report to the EPC (Brown Evidence-based Practice Center, Contract No. 75Q80120D00001).

AHRQ EPC reviews provide comprehensive, science-based information on common, costly medical conditions, and new healthcare technologies and strategies.

The Patient-Centered Outcomes Research Institute^® (PCORI^®) was established to fund research that helps patients and caregivers make better informed healthcare choices. To fulfill its authorizing mandate, PCORI partners with AHRQ to generate evidence synthesis products and make comparative effectiveness research more available to patients and providers.

Systematic reviews are the building blocks underlying evidence-based practice; they focus attention on the strength and limits of evidence from research studies about the effectiveness and safety of a clinical intervention. In the context of developing recommendations for practice, systematic reviews can help clarify whether assertions about the value of the intervention are based on strong evidence from clinical studies. For more information about AHRQ EPC systematic reviews, see https://effectivehealthcare.ahrq.gov/about/epc/evidence-synthesis.

AHRQ expects that the EPC evidence reports and technology assessments, when appropriate, will inform individual health plans, providers, and purchasers as well as the healthcare system as a whole by providing important information to help improve healthcare quality. Transparency and stakeholder input are essential to the Effective Health Care Program. Please visit the website (www.effectivehealthcare.ahrq.gov) to see draft research questions and reports or to join an email list to learn about new program products and opportunities for input.

If you have comments on this systematic review, they may be sent by mail to the Task Order Officer named below at: Agency for Healthcare Research and Quality, 5600 Fishers Lane, Rockville, MD 20857, or by email to vog.shh.qrha@cpe.

• Robert Otto Valdez, Ph.D., M.H.S.A.
  Director
  Agency for Healthcare Research and Quality
• Nakela Cook, M.D., M.P.H.
  Executive Director
  Patient-Centered Outcomes Research Institute
• Craig A. Umscheid, M.D., M.S.
  Director
  Evidence-based Practice Center Program
  Center for Evidence and Practice Improvement
  Agency for Healthcare Research and Quality
• Therese Miller, Dr.P.H.
  Acting Director
  Center for Evidence & Practice Improvement
  Agency for Healthcare Research and Quality
• William Lawrence, M.D., M.S.
  Senior Clinical Advisor
  Office of the Chief Engagement and Dissemination Officer
  Patient-Centered Outcomes Research Institute
• Jill Huppert, M.D., M.P.H.
  Task Order Officer
  Center for Evidence and Practice Improvement
  Agency for Healthcare Research and Quality
• Michelle Althuis, Ph.D.
  Associate Director
  Research Synthesis
  Patient-Centered Outcomes Research Institute
• Jennie Dalton, M.P.H.
  Program Officer
  Research Synthesis
  Patient-Centered Outcomes Research Institute