DUMC Library: 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?
- Were patients randomized?
- Was randomization concealed?
- Were patients analyzed in the groups to which they were
randomized?
- 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?
- Were 5 important groups (patients, caregivers, collectors of outcome data, adjudicators of outcome,
data analysts) aware of group allocation?
- Aside from the experimental intervention, were the groups
treated equally?
- Was follow-up complete?
What are the results?
- How large was the treatment effect?
- How precise was the estimate of the treatment effect?
How can I apply the results to my patient care?
- Were the study patients similar to my patients?
- Were all patient important outcomes considered?
- Are the likely benefits worth the potential harms and costs?
Estimating the size of the treatment effect
| | Outcome
Yes | Outcome
No |
| Treated (Y) | a | b |
| Control (X) | c | d |
Risk of Outcome: Y = a/(a+b)
Risk of Outcome: X = c/(c+d)
- Relative Risk (RR) is the risk of the outcome in the treated group (Y) compared to
the risk in the control group. RR = Y/X
- Relative Risk Reduction (RRR) is the percent reduction in risk in the treated group (Y)
compared to the control group (X). RRR = 1-RR x 100%
- Absolute Risk Reduction (ARR) is the difference in risk between the control group (X)
and the treatment group (Y). ARR = X-Y
- Number Needed to Treat (NNT) is the number of patients that must be treated over a given period of
time to prevent one adverse outcome. NNT = 1/ARR
Finding articles about therapy
PubMed:
- Use Clinical Queries for therapy
- Limit to publication type: randomized controlled trial
Ovid:
- Limit to clinical trial.pt. (publication type)
- EBM Filter under Saved Searches: EBMRCTF
- EBM Filter under Saved Searches: EBMTX1 (comprehensive/sensitivity)
- EBM Filter under Saved Searches: EBMTX2 (relevance/specificity)
References:
- JAMA 1993 270:2598-2601
- JAMA 1994 271:59-63
- ACP Journal Club 1994 Jul-Aug A10-A12
From: Guyatt, G. Users' Guides to the Medical Literature: Essentials of Evidence-based Clinical Practice.
AMA Press, 2002 and Sackett, D.L. Evidence-Based Medicine. How to Practice and Teach EBM. Churchill-Livingstone,
2nd edition, 2001 (pocket cards).
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Last modified on: 16-Dec-04