The document provides an introduction to evidence-based medicine (EBM). It defines EBM as using the best current evidence from clinical research in medical decision making. EBM requires considering both research evidence and a patient's values and preferences. Reliable evidence comes from systematic reviews and meta-analyses of multiple studies rather than individual studies or expert opinions. Practicing EBM involves forming a clear clinical question, finding the best evidence, critically evaluating it, and applying the results to patient care. While evidence-based studies aim to be rigorous, their results could still mislead due to biases or other limitations if not properly appraised.

1. An Introduction to Evidence
Based Medicine
Paul Albert
Weill Cornell Medical College
August 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 specific
condition 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 EBM
1. 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 Scenario
Julia Wang is a 55-year old woman. She has
recently been diagnosed with rheumatoid arthritis
and wants to control her symptoms of joint pain.

15. Get Answers to Any Background
Questions at MedlinePlus:
http://medlineplus.gov

16. Ask a Clinical Question
Julia Wang is a 55-year old woman. She has
recently been diagnosed with rheumatoid arthritis
and wants to control her symptoms of joint pain.
For a 55-year old woman with rheumatoid
arthritis, will taking Remicade reduce joint pain as
compared to other treatments?

17. Answer Your Clinical Question Using
Clinical Queries at PubMed.Com

19. Or, use TRIP Database located at
http://www.tripdatabase.com

22. The next two steps we don’t have
time for: critically appraise the
study and apply to patient care.

23. 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.

24. Timeline of Hormone
Replacement Therapy
1966 – Publication of, Feminine Forever, book which says that
women can escape the “horror” of menopause by taking
hormone replacement therapy (HRT).
1960s and 70s – Estrogen sales triple in the United States.
1970s and 80s – HRT is used against osteoporosis but early
indications suggest that HRT causes breast cancer.
1980s and 90s – Observational studies seem to show that HRT
protects 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 of
estrogen and progestin. The study shows that women taking
HRT have higher risk of breast cancer, stroke, and heart
disease.

25. 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.

26. “50% of studies are wrong.”
John P. A. Ioannidis, PLoS
Medicine, PMID: 16060722