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Medical Students
Evidence-based Medicine

Steps of EBM:
  1. Converting the need for information (about prevention, diagnosis, prognosis, therapy, causation, etc.) into an answerable question.
  2. Tracking down the best evidence with which to answer that question.
  3. Critically appraising that evidence for its validity (closeness to the truth), impact (size of the effect), and applicability (usefulness in our clinical practice).
  4. Integrating the critical appraisal with our clinical expertise and with our patient's unique biology, values and circumstances.
  5. Evaluating our effectiveness and efficiency in executing steps 1-4 and seeking ways to improve them both for next time.

Asking Answerable Questions:
Distinguishing between background and foreground questions 
Make sure your questions have these components:

  1. The patient and/or problem of interest
  2. The main intervention (defined very broadly, including an exposure, a diagnostic test, a prognostic factor, a treatment, a patient perception, and so forth)
  3. Comparison intervention(s), if relevant
  4. The clinical outcome(s) of interest

For example: In a patient with a family history of a first degree relative with breast cancer, what is the yield of staring mammographic screening earlier compared with usual screening?

Systematically Searching the Medical Literature:
Rhona Kelley or staff from the medical library will do a hands-on tutorial in the afternoon to review systematic searching of databases. The focus will be on searching Medline, specifically using MESH headings and the Clinical Queries search options. There will also be a quick review of the Cochrane Database and InfoRetriever and InfoPOEMS databases.

Critically Appraising the Medical Literature and Applying the Evidence:
The important and common types of articles that you will need to learn how to appraise and apply are those that deal with therapy, prevention, diagnostic tests, harm and prognosis. Make sure that the article you appraise is evidence that attempts to answer your clinical question. Determine what kind of article it is and what clinical outcomes it measures and seeks to answer, and then use the critical appraisal charts and references distributed at orientation to do your appraisal and help you apply the evidence to your patient or patient population.

The following are terms and concepts used commonly in clinical epidemiology; you should be familiar with their meanings as you prepare for the presentation.

Definitions in Clinical Epidemiology:
The definitions given here are taken in part from Epidemiology for the Health Sciences by DF Austin and SB Werner, and a Dictionary of Epidemiology (2nd ed.) edited by JM Last.

Bias - Non-random deviation of results from the truth. There are many causes of bias caused by flaws in study design and data collection, analysis, and interpretation. There is no implication that biasis pejorative although it may be.
Case-control Study - An epidemiologic study in which one collects a group of people with a certain disease (cases) to compare with another group of people without that disease (controls) to see if some factor (suspected of being a cause) is more common in the disease group. Most important is the fact that people must already have the disease to be chosen as cases. The outcome is expressed as an 'odds ratio'.
Clinical Significance - The statement that something is clinically important.
Cohort Study - A study in which individuals are identified who have or have not been exposed to something of interest (asbestos in the workplace, hypertension) and are then followed over time to see if they develop a particular outcome (pleural mesothelioma, stroke). 
Confounding Variable - A variable that effects the outcome of interest but is not related to the factor under investigation. For example, going to cardiac rehabilitation after a heart attack decreases your chances of dying of heart disease but this result is confounded by the fact that people who look after themselves generally are more likely to go to rehabilitation and less likely to die of heart disease.
Control Group - The comparison group used in a study.
Exclusion Criteria - the criteria that are established to decide which patients are excluded from a study or trial (alcoholics, those who have not kept appointments in the past). Generalization - the ability to extrapolate from the results of a trial or study to patients who were not included in it.
Inclusion Criteria - The criteria that are established to decide which patients are included in a study or trial (white males with hypertension, post-menopausal women with breast cancer).
Intent-to-treat Analysis - An analysis of data based on the group to which the patient was originally assigned, not the group in which the patient ended up.
Randomization - The allocation of individuals to groups by chance. Within the limits of chance variation, randomization should make the control and experimental groups similar. 
Statistical Significance - Statistical methods allow an estimate to be made of the probability of the observed or greater degree of association between independent and dependent variables under the null hypothesis. From this estimate, in a sample of given size, the statistical significance of a result can be stated. Usually the level of the statistical significance is stated by the p-value.
 

Other Resources
The following books and series of articles, explain a lot of the concepts that the student will need to understand. The student is not expected to read any or all of these, but might find them helpful in answering specific questions.
 
Sackett DL, Haynes RB, Guyatt GH, Tugwell P. Clinical Epidemiology: A Basic Science for Clinicians (2nd Edition). Little, Brown and Co.; Boston: 1991. 
Fletcher RH, Fletcher SW, Wagner EH. Clinical Epidemiology: The Essentials (2nd Edition). Williams & Wilkins; Baltimore: 1988. 
Sackett DL, Richardson WS, Rosenberg W, Haynes RB. Evidence Based Medicine: How to Practice and Teach EBM. Churchill Livingstone; New York:     1997. 
Eddy DM. Clinical Decision Making: From Theory to Practice. Jones and Bartlett Publishers; Sudbury, Mass.: 1996. 
Greenhalgh T. How to Read a Paper: The Medline Database. BMJ 1997 Jul19;315(7101):180-183. 
Greenhalgh T. How to Read a Paper: Getting Your Bearings (deciding what the paper is about). BMJ 1997 Jul 26;315(7102):243-246. 
Greenhalgh T. How to Read a Paper: Assessing the Methodological Quality of Published Papers. BMJ 1997 Aug 2;315(7103):305-308. 
Greenhalgh T. How to Read a Paper: Statistics for the Non-Statistician. I: Different Types of Data Need Different Statistical Tests. BMJ 1997 Aug9;315(7104):364-367. [Erratum appears in: BMJ 1997 Sep 13;315(7109):675.] 
Greenhalgh T. How to Read a Paper: Statistics for the Non-Statistician. II: "Significant" Relations and Their Pitfalls. BMJ 1997 Aug 16;315(7105):422-425. 
Greenhalgh T. How to Read a Paper: Papers That Report Drug Trials. BMJ 1997 Aug 23;315(7106):480-483. 
Greenhalgh T. How to Read a Paper: Papers That Report Diagnostic or Screening Tests. BMJ 1997 Aug 30;315(7107):540-543. 
Greenhalgh T. How to Read a Paper: Papers That Tell You What Things Cost (economic analysis). BMJ 1997 Sep 6;315(7108):596-599. 
Greenhalgh T. How to Read a Paper: Papers That Summarize Other Papers (systematic reviews and meta-analyses). BMJ 1997 Sep     13;315(7109):672-675. 
Greenhalgh T, Taylor R. How to Read a Paper: Papers That Go Beyond the Numbers (qualitative research). BMJ 1997 Sep 20;315(7110):740-743.

NOTES:
  1. Guyatt GH, Sackett DL, Cook DJ, for the Evidence-based Medicine Working Group. Users' Guide to the Medical Literature: II. How to Use an Article About Therapy or Prevention: A. Are the results of the study valid? JAMA 1993 Dec 1; 270(21): 2598-2601.
  2. Guyatt GH, Sackett DL, Cook DJ, for the Evidence-based Medicine Working Group. Users' Guide to the Medical Literature: II. How to Use an Article About Therapy or Prevention: B. What were the results and will they help me in caring for my patients? JAMA 1994 Jan 5; 271(1): 59-63.
  3. Jaeschke R, Guyatt GH, Sackett DL, for the Evidence-based Medicine Working Group. Users' Guide to the Medical Literature: III. How to Use an Article About a Diagnostic Test: A. Are the results of the study valid? JAMA 1994 Feb 2; 271(5): 389-391.
  4. Jaeschke R, Guyatt GH, Sackett DL, for the Evidence-based Medicine Working Group. Users' Guide to the Medical Literature: III. How to Use an Article About a Diagnostic Test: B. What are the results and will they help me in caring for my patients? JAMA 1994 Mar 2; 271(9): 703-707.
  5. Levine M, Walter S, Lee H, Haines T, Holbrook A, Moyer V, for the Evidence Based Medicine Working Group. User's Guide to the Medical Literature:
    IV. How to Use an Article About Harm. JAMJ 1994 May 25; 271(20): 1615-1619.
    1. Laupacis A, Wells G, Richardson S, Tugwell P, for the Evidence Based Medicine Working Group. User's Guide to the Medical Literature: V. How to Use an Article About Prognosis. JAMA 1994 Jul 20; 272(3): 234-237. 


    Evaluating an Article about Therapy or Prevention:

    Name of article
    Are the results of this single preventive of therapeutic trial valid?
    Main questions;
    Was the assignment of patients to treatments randomized?  And was the randomization list concealed?
    Was follow-up sufficiently long and was it complete?
    Were all patients analyzed in the groups to which they were randomized?

    Secondary questions;
    Were patients, health workers, and study personnel "blind" to treatment?
    Aside from the experimental intervention, were the groups treated equally?
    Were the groups similar at the start of the trial?

    Will the valid, important results help me in caring for my patients?
    How large was the treatment effect?
    How precise was the estimate of the treatment effect?
    Are my patients so different from the patients included in this trial that the results can't apply?
    Is the treatment feasible ("doable") in my practice?
    Are the likely treatment benefits worth the potential harms and costs?
    Are there important issues with respect to my patient's wishes or expectations that are not considered in this trial?         Not applicable to this exercise.

    What are the major strengths and weaknesses of this article?


    Evaluating an Article about a Diagnostic Test:

    Name of article:
    Are the results of this diagnostic study valid?
    Was there an independent, blind comparison with a reference ("gold") standard?
    Did the patient sample include an appropriate selection of patients to whom the diagnostic test will be applied in clinical practice?
    Was the reference standard done on all the patients (as opposed to being done selectively only on patients in whom the new diagnostic test was positive or negative)?
    Were the methods for performing the test described in sufficient detail to permit replication?
    Was the test (or tests) validated in a second, independent group of patients?

    Does the valid evidence about this diagnostic test allows us to accurately distinguish between patients who have or don't have a condition?
    Are the likelihood ratios for the test presented or data necessary for their calculation provided?

    Can I use this valid, important diagnostic test in my practice?
    Is the test available, affordable, and reproducible in my practice setting?
    Can I generate clinically sensible estimates of the pre-test probability of disease for my patients?
    Will using this test change my management of this disease or condition?
    Will my patients be better off as a result of the test?

    What are the major strengths and weaknesses of this article?


    Evaluating an Article about Harm/Etiology:

    Name of article:
    Were there clearly defined comparison groups that were similar with respect to important determinants of outcome, other than the one of interest?
    Were the treatments/exposures and outcomes measured in the same way in the groups being compared?
    Was the follow-up of patients sufficiently long and complete for the outcome to occur?
    Is the temporal relationship correct?
    Is there a dose response relationship?

    Are the valid results of this harm study important?
    What is the magnitude and precision of the association between exposure and outcome?

    Can this valid and important evidence about harm be applied to my patients?
    Are my patients so different from those included in this study that the results don't apply?
    Are my patients at risk for the adverse outcome? What are thier potential benefits from the therapy or exposure?
    Are there alternative treatments/exposures available?
    Are there important issues with respect to my patient's wishes or expectations that are not considered in this trial?     Not applicable to this exercise

    What are the major strenths and weaknesses of this article?


    Evaluating an Artcle about Prognosis:

    Name of article:

    Is this evidence about prognosis valid?
    Was a well-defined, representative sample of patients assembled at a similar (usually early) point in the course of their disease?
    Was patient follow-up sufficiently long and complete?
    Were objective and unbiased outcome criteria used? Were these applied in a "blind" fashion?
    If sub-groups with different prognosis were identified, was there adjustment for important prognostic factors?  Was there alidation in an independent group of patients?

    Is this valid evidence about prognosis important?
    How large is the likelihood of the outcome event(s) in a specified period of time?
    How precise is the estimate of the likelihood?

    Can we apply this valid, important evidence about prognosis to our patients?
    Were the study patients similar to our own?
    Will the results lead directly to selecting or avoiding therapy?
    Are the results useful for reassuring or counseling patient?

    What are the major strengths and weaknesses of this article? 

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