DUMC Library: Evaluating a HARM article

Validity issues

Did experimental and control groups begin the study with a similar prognosis?
1. Did the investigators demonstrate similarity in all known determinants of outcome? Did they adjust for differences in the analysis?
2. Were exposed patients equally likely to be identified in the two groups?

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

3. Were the outcomes and exposures measured in the same way in the groups being compared?
4. Was follow-up sufficiently complete?

What are the results?

1. How strong is the association between exposure and outcome?
2. How precise is the estimate of risk?

How can I apply the results to my patient care?

1. Were the study patients similar to the patient in my practice?
2. Was the duration of follow-up adequate?
3. What was the magnitude of the risk?
4. Should I attempt to stop the exposure?

Strength of inference

RCT or Prospective cohort studies:

• Relative Risk (RR) is the risk of the outcome in the exposed group divided by the risk of the outcome in the unexposed group: RR = a/(a + b) divided by c/(c + d)
  "RR of 3.0 means that the outcome occurs 3 times more often in those exposed versus unexposed."

Case-control studies:

• Odds Ratio (OR) is the odds of previous exposure in subjects with the outcome divided by the odds of exposure in subjects without the outcome: OR = (a/b) divided by (c/d) = ad/bc
  "OR of 3.0 means that cases were 3 times more likely to have been exposed than were control patients."

Confounding variable is one whose influence distorts the true relationship between a potential risk factor and the clinical outcome of interest.

Finding articles about harm

• Use Clinical Queries for Etiology
• Search term: risk

• risk.mp. (MeSH or textword)
• explode Cohort Studies/ (MeSH)
• EBM Filter under Saved Searches: EBMET1 (comprehensive/sensitivity)
• EBM Filter under Saved Searches: EBMET2 (relevance/specificity)

References:

• JAMA 1994 271:1615-1619
• ACP Journal Club 1994 Nov-Dec; A10-A11