MUSM Libraries: Evaluating a THERAPY article

Validity issues |  Estimating the size of treatment effect |  Finding articles

Validity issues

Are the results valid?
Did experimental and control groups begin the study with a similar prognosis?

  1. Were patients randomized?
  2. Was randomization concealed?
  3. Were patients analyzed in the groups to which they were randomized?
  4. Were patients in the treatment and control groups similar with respect to known prognostic factors?

Did experimental and control groups retain a similar prognosis after the study started?

  1. Were 5 important groups (patients, caregivers, collectors of outcome data, adjudicators of outcome, data analysts) aware of group allocation?
  2. Aside from the experimental intervention, were the groups treated equally?
  3. Was follow-up complete?

What are the results?

  1. How large was the treatment effect?
  2. How precise was the estimate of the treatment effect?

How can I apply the results to my patient care?

  1. Were the study patients similar to my patients?
  2. Were all patient important outcomes considered?
  3. Are the likely benefits worth the potential harms and costs?

Estimating the size of the treatment effect

Treated (Y) a b
Control (X) c d

Risk of Outcome: Y = a/(a+b)
Risk of Outcome: X = c/(c+d)

Experimental group size:
Control group size:
Events in experimental group:
Events in control group:


Finding articles about therapy

PubMed for Handhelds (Memorial On-Campus/Remote One and Mercer On-Campus access)
PubMed for Handhelds (Mercer Off-Campus access)


From: Guyatt, G. Users' Guides to the Medical Literature: Essentials of Evidence-based Clinical Practice. AMA Press, 2002 and Straus. Evidence-Based Medicine. How to Practice and Teach EBM. Churchill-Livingstone, 3rd edition, 2005 (pocket cards).

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