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?
- 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)
- Absolute Risk Reduction (ARR) is the difference in risk
between the control group (X) and the treatment group (Y). ARR =
X-Y
- Control Event Rate (CER)
The proportion of patients in the
control group who experience the studied event.
- Experimental Event Rate (EER)
The proportion of patients
in the experimental treatment group who are observed to experience the outcome
of interest.
- 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
- Odds Ratio (OR)
The ratio of the odds of having the target
disorder in the experimental group relative to the odds in favor of having the
target disorder in the control group (in cohort studies or systematic reviews)
or the odds in favor of being exposed in subjects with the target disorder
divided by the odds in favor of being exposed in control subjects (without the
target disorder).
- 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%
Finding articles about therapy
PubMed:
PubMed for
Handhelds (Memorial On-Campus/Remote One and Mercer On-Campus access)
PubMed for
Handhelds (Mercer Off-Campus access)
- Select Search MEDLINE/PubMed and choose Therapy from the
Categories under Clinical Queries.
- For Randomized Controlled Trials, choose Search MEDLINE/PubMed
and use the Search with no filters and enter your search term/s AND
randomized controlled trial. Alternatively, select PICO search and
choose Randomized Controlled Trial from the Publication type drop down
menu.
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 Straus. Evidence-Based
Medicine. How to Practice and Teach EBM. Churchill-Livingstone, 3rd
edition, 2005 (pocket cards).
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