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Evidence-Based Medicine Critical Appraisal of Harm. Department of Medicine - Residency Training Program Tuesdays, 9:30 a.m. - 12:00 p.m., UW Health Sciences Library. Steps in Practicing EBM. Convert the need for information into an answerable question.

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evidence based medicine critical appraisal of harm

Evidence-Based MedicineCritical Appraisal of Harm

Department of Medicine - Residency Training Program

Tuesdays, 9:30 a.m. - 12:00 p.m., UW Health Sciences Library

steps in practicing ebm
Steps in Practicing EBM
  • Convert the need for information into an answerable question.
  • Track down the best evidence with which to answer that question.
  • Critically appraise the evidence for its validity, impact, and applicability.
  • Integrate the evidence with our clinical expertise and our patient’s characteristics and values.
steps in practicing ebm1
Steps in Practicing EBM
  • Convert the need for information into an answerable question.
  • Track down the best evidence with which to answer that question.
  • Critically appraise the evidence for its validity, impact, and applicability.
  • Integrate the evidence with our clinical expertise and our patient’s characteristics and values.
slide6
Good questions are the backbone of practicing EBM. It takes practice to ask the well-formulated question.
well built clinical s
Well-Built Clinical ?’s
  • Directly relevant to the care of the patient and our knowledge deficit.
  • Contains the following elements:
    • the patient or problem being addressed
    • the intervention or exposure being considered
    • the comparison intervention or exposure, when relevant
    • the clinical outcomes of interest.
well formulated s
Well Formulated ?’s
  • Focus scarce learning time on evidence directly relevant to patient’s needs and our particular knowledge needs.
  • Suggest high-yield search strategies.
  • Suggest forms that useful answers might take.
  • Help us to model life-long learning techniques for our colleagues and students.
  • Are answerable and, thus, reinforce the satisfaction of finding evidence that makes us better, faster clinicians.
steps in practicing ebm2
Steps in Practicing EBM
  • Convert the need for information into an answerable question.
  • Track down the best evidence with which to answer that question.
  • Critically appraise the evidence for its validity, impact, and applicability.
  • Integrate the evidence with our clinical expertise and our patient’s characteristics and values.
general resources

MeSH Headings

General Resources

META-SEARCH ENGINES

PrimeAnswers

TRIP+

SUMSearch

SYSTEMATIC REVIEWS/META-ANALYSES

Cochrane Library

PubMed Clinical Queries

EVIDENCE GUIDELINES/SUMMARIES

AHRQ Evidence Reports

Clinical Evidence

AHRQ Preventive Services

CLINICAL RESEARCH CRITIQUES

ACP Journal Club 1996-

Bandolier 1994-

BestBETs

CASE REPORTS/SERIES, PRACTICE GUIDELINES, ETC

National Guideline Clearinghouse

PubMed

steps in practicing ebm3
Steps in Practicing EBM
  • Convert the need for information into an answerable question.
  • Track down the best evidence with which to answer that question.
  • Critically appraise the evidence for its validity, impact, and applicability.
  • Integrate the evidence with our clinical expertise and our patient’s characteristics and values.
judging validity with just 4 questions
Judging validity with just 4 questions!

1. Did investigators assemble clearly defined groups of patients similar in all important ways other than exposure?

2. Were exposures and outcomes measured in the same ways in both groups (objective/blinded)?

3. Was follow-up sufficiently long and complete (5% and 20% rule)?

4. Do the results of the harm study fulfill some of the tests for “causation”?

types of studies in order of decreasing likelihood of being valid

*

*

Types of Studies(in order of decreasing likelihood of being valid)
  • Systematic reviews are ideal because individual RCTs seldom large enough to detect rare adverse events with precision - unfortunately, SR are uncommon.
  • RCTs are difficult to conduct for most studies of harm.
  • Cohort studies - exposed and unexposed followed for development of outcome of interest.
  • Case-control studies - cases with outcome of interest compared with controls for “exposure”.
  • Cross-sectional studies.
  • Case reports.
criteria for inferring causality
Criteria for Inferring Causality
  • Is it clear that the exposure preceded the onset of the outcome?
  • Is there a dose-response relationship?
  • Any positive evidence from a dechallenge-rechallenge study?
  • Is the association consistent across studies?
  • Does the association have biological plausability?
judging clinical importance with just 2 questions
Judging clinical importance with just 2 questions!

1. What is the magnitude of the treatment effect?

RR = (Exposed ER - Unexposed ER)/Unexposed ER

AR difference = Exposed ER - Unexposed ER

NNH = 1/AR difference

2. How precise is this estimate of the treatment effect?

95% CI - range of values within which we can be 95% sure that the population value lies.

calculating nnt nnh
Calculating NNT/NNH

1. A randomized trial of new drug “Ligatite” reveals that 25% of World Cup skiers who take the drug for one year have ACL tears whereas 50% of World Cup skiers who take the placebo for the year have ACL tears. What is the NNT?

NNT = 1/AR reduction = 1/(0.50-0.25) = 4

2. The study of the drug “Ligatite” also notes that 20% of athletes taking the drug develop clinical depression whereas 10% of athletes taking the placebo develop depression. What is the NNH?

NNH = 1/AR increase = 1/(0.20-0.10) = 10

3. An advertisement for a new drug fails to mention that it increases the relative risk of myocardial infarction by 50 % over 5 years. You read a valid study describing this finding. What is the NNH?

Unknown without knowing the event rate in the control population.

the odds ratio
The Odds Ratio
  • Used as an estimate of the risk ratio if the risk of the disease in a population is low.
  • Is the principle measure of effect from case-control studies (cannot calculate event rates). Also used to report effect size in meta-analysis.
  • Odds of exposure in the disease group divided by odds of exposure in non-diseased group.

OR = (a/c)/(b/d)

= ad/cb

slide22

Converting OR to NNH

Calculator available at:

http://www.cebm.utoronto.ca/practise/ca/statscal/orToNnt.htm

avoiding tiv table induced vertigo
Avoiding TIV(table induced vertigo)
  • OR’s greater than 1.5 produce NNH < 50 across most PEER’s
  • Patient needs to be at risk (non-trivial PEER) in order to be concerned.
  • for any OR, NNH greatest when PEER=0.5
  • Consider carefully nature of harm (are your patient’s values disrupted by the intervention and its sequelae)
estimating our patient s expected event rates peer
Estimating Our Patient’s Expected Event Rates (PEER)

1. Assign our patient the overall control event rate from the study.

2. If there is a subgroup of patients in the study with similar characteristics assign the event rate for that subgroup.

3. If a validated clinical predication guide is available use it to assign an event rate.

4. Look for a different paper that describes the prognosis of untreated patients more similar to our patient and use its results to assign an event rate.

clinical tools for estimating peer
Clinical Tools for Estimating PEER

Available at: http://hin.nhlbi.nih.gov/atpiii/calculator.asp?usertype=prof%09

applicable to our patient
Applicable to Our Patient?

1. Is our patient so different from those in the study that its results cannot apply?

2. What is our patient’s risk of benefit and harm from agent?

3. What are our patient’s preferences, concerns, and expectations from this treatment?

4. What alternative treatments are available?

returning to ligatite
Returning to “Ligatite”

The trial of the drug revealed that 25% of World Cup skiers who take the drug for 1 year have ACL tears whereas 50% of skiers who take the placebo have ACL tears. It also revealed that 20% of exposed skiers developed depression whereas 10% of unexposed skiers developed depression.

Your patient reads about this in Ski Magazine and asks you to write a prescription. In discussing the medication with her you want to provide her with an estimate of the magnitude of risk reduction she would realize. Is her NNT = 4 and should she take this medication?

Probably Not:

1. Her risk of an ACL tear is substantially less so you have to re-estimate her expected event rate.

2. She is unlikely to be skiing year round so NNT is at least 2 to 3 times as high.

3. There is risk of developing depression (NNH = 10 over 1 year).

4. Whether or not to take the drug should take into account the relative value to the patient of preventing an ACL tear faced with the probability of developing depression.