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Introduction to Evidence Based Medicine


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  • 1. An Introduction to EvidenceBased MedicinePaul AlbertWeill Cornell Medical CollegeAugust 27, 2009
  • 2. What is Evidence Based Medicine (EBM)?• Definition = use of current best evidence in making decisions about the care of individual patients• sometimes used synonymously with “Evidence Based Practice”• requires an understanding of a patient’s values and circumstances
  • 3. What EBM is Not• An expert opinion• Statement in a textbook• What the latest paper in a prestigious journal says• Traditional approach – “The way we have always done it”• Continuing Medical Education course• Choosing the most expensive treatment the patient can afford
  • 4. Evidence-Based Pyramid Typically prospective observational studies, not randomized Patients who already have a specificcondition are compared Collection of reports, with those who don’t no control group
  • 5. Systematic Review• A summary of the medical literature that uses well- defined methods to systematically search, critically appraise, and synthesize the world literature on a specific issue or question.• Best systematic reviews follow a specific set of rules• The most well-known creator of systematic reviews is the Cochrane Collaboration.• West China Hospital should be very proud to be a Cochrane Center.
  • 6. Meta-Analysis• A statistical technique in which the results of numerous studies are mathematically combined in order to improve the reliability of the results.• Meta-analyses and systematic reviews are different.
  • 7. Steps for Practicing EBM1. Convert the need for information into an answerable clinical question.2. Find the best evidence.3. Critically appraise the evidence.4. Apply to patient care.
  • 8. Step #1: Ask a Clinical Question• Create a clinical question, which can lead directly to a well-built search strategy.• Example: “For a 55-year old woman with rheumatoid arthritis, will taking Remicade reduce joint pain?”• Question types: therapy, prognosis, diagnosis, harm• Note: sometimes you have basic “background” questions. These you can answer by visiting MedlinePlus.
  • 9. Step #2: Find the Best Evidence• Create a search strategy. For example: “Remicade AND rheumatoid arthritis”• Perform your search in a database of the medical literature such as PubMed Clinical Queries or TRIP Database.
  • 10. Step #3: Critically Appraise the Evidence• What is the impact (size of the effect)? What is the confidence interval?• What is the validity (extent to which conclusions follow from the methods)?• Are the results consistent across different studies?• Did the study choose a relevant outcome?• Every study is based on a series of assumptions. What are those assumptions? To what extent are they valid?• Much of the critical appraisal work is done by assessing the “Methods” section of a paper.
  • 11. Common Features of High Quality Evidence Based Studies• large number of subjects• subjects assigned to groups randomly• double-blinded• placebo-controlled• prospective• low loss to follow-up (<20%)• replicated across multiple centers
  • 12. Step #4: Apply to Patient Care• What is the relevance of the study to your patient? (Few studies are 100% relevant!)• For example: to what extent is the study population similar to your patient population?• What kind of treatment or harm effect does the study identify? Is the effect clinically significant or merely statistically significant?• For therapies, what about side effects?• How do your patient’s personal preferences inform your decision-making?• What about cost?
  • 13. Why Even Evidence-Based Studies Could Be Misleading• Publications bias• Failure to account for long-term outcomes• A study uses a misleading intermediary outcome (example: cholesterol vs. cardiovascular disease)• Statistical chance• Excessive cleverness with statistics• “Ghost writers”• Industry funding (studies are expensive!)
  • 14. Sample ScenarioJulia Wang is a 55-year old woman. She hasrecently been diagnosed with rheumatoid arthritisand wants to control her symptoms of joint pain.
  • 15. Get Answers to Any Background Questions at MedlinePlus:
  • 16. Ask a Clinical QuestionJulia Wang is a 55-year old woman. She hasrecently been diagnosed with rheumatoid arthritisand wants to control her symptoms of joint pain.For a 55-year old woman with rheumatoidarthritis, will taking Remicade reduce joint pain ascompared to other treatments?
  • 17. Answer Your Clinical Question Using Clinical Queries at PubMed.Com
  • 18. Or, use TRIP Database located at
  • 19. The next two steps we don’t have time for: critically appraise the study and apply to patient care.
  • 20. Hormone Replacement Therapy (HRT)• Definition = medications which artificially raise levels of sex hormones• Until recently, HRT was widely used in the West among menopausal and post-menopausal women.
  • 21. Timeline of Hormone Replacement Therapy1966 – Publication of, Feminine Forever, book which says thatwomen can escape the “horror” of menopause by takinghormone replacement therapy (HRT).1960s and 70s – Estrogen sales triple in the United States.1970s and 80s – HRT is used against osteoporosis but earlyindications suggest that HRT causes breast cancer.1980s and 90s – Observational studies seem to show that HRTprotects against disease. This is later shown to be wrong.1996 – Premarin is the best-selling prescription drug in the U.S.2002 – Decision to halt the “Women’s Health Initiative” study ofestrogen and progestin. The study shows that women takingHRT have higher risk of breast cancer, stroke, and heartdisease.
  • 22. More about the 2002 Women’s Health Initiative Study• Before 2002, a number of studies seemed to show that HRT was protective against disease.• But – these studies were observational and were conducted on self-selected patients, people who were generally healthier than most.• In 1997 or so, a researcher said, “We are going to do what we have been too lazy or unwilling to do: test the hypothesis that HRT protects against disease.”• The WHI study was the first large-scale double- blind placebo-controlled study and it showed HRT causes harm.
  • 23. “50% of studies are wrong.” John P. A. Ioannidis, PLoS Medicine, PMID: 16060722