Critiquing for Evidence-based Practice: Therapy or Prevention
M8120Columbia University
Suzanne Bakken, RN, DNSc
Critical Analysis of Therapy or Prevention Studies
Are the results of the study valid?
What are the results?Will the results help me in caring
for my patients?
Critical Analysis of Therapy or Prevention Studies
Are the results of the study valid?– Was the assignment of patients to
treatment randomized?
Critical Analysis of Therapy or Prevention Studies
Are the results of the study valid?– Were all patients who entered the
trial properly accounted for and attributed at its conclusion?–Follow-up complete– Intent to treat analysis
Critical Analysis of Therapy or Prevention Studies
Are the results of the study valid?– Were patients, their clinicians,
study personnel “blind” to treatment?
Critical Analysis of Therapy or Prevention Studies
Are the results of the study valid?– Were the groups similar at the
start of the trial?
Critical Analysis of Therapy or Prevention Studies
Are the results of the study valid?– Aside from the experimental
intervention, were the groups treated equally?
Critical Analysis of Therapy or Prevention Studies
Are the results of the study valid?
What are the results?Will the results help me in caring
for my patients?
Critical Analysis of Therapy or Prevention Studies
What are the results?Focus on clinical rather than
statistical significance?– How large was the treatment effect?– How precise was the estimate of the
treatment effect?– RR, RRR, CI, etc.
Critical Analysis of Therapy or Prevention Studies
Risk without therapy (Baseline)= X Risk with therapy = Y Absolute Risk Reduction(ARR) (risk difference) = X - Y Relative risk (RR) = Y/X Relative risk reduction (RRR)=X-Y (ARR)/X (baseline) *
100 Confidence interval (CI) = range that includes the true
RRR a set percentage of time
Critical Analysis of Therapy or Prevention Studies
Death = 20% in control group and 15% in experimental
How large was the treatment effect?– Risk without therapy (Baseline)= X– Risk with therapy = Y– Absolute Risk Reduction(ARR) (risk difference) = X -
Y– Relative risk (RR) = Y/X– Relative risk reduction (RRR)=X-Y (ARR)/X
(baseline) * 100
Critical Analysis of Therapy or Prevention Studies
Target disorder – Type I diabetes Rx – intensive insulin treatment Event prevented (Diabetic retinopathy) = 9.6% in
control group and 2.8% in experimental How large was the treatment effect?
– Risk without therapy (Baseline)= X– Risk with therapy = Y– Absolute Risk Reduction(ARR) (risk difference) = X -
Y– Relative risk reduction (RRR)=X-Y (ARR)/X
Critical Analysis of Therapy or Prevention Studies
Target disorder – Type I diabetes Rx – intensive insulin treatment Event prevented (Diabetic retinopathy) = 9.6% in
control group and 2.8% in experimental How large was the treatment effect?
– Risk without therapy (Baseline)= X=.096– Risk with therapy = Y=. 028– Absolute Risk Reduction(ARR) (risk difference) = X
– Y = .068– Relative risk reduction (RRR)=X-Y (ARR)/X = .71
Critical Analysis of Therapy or Prevention Studies
Target disorder – independent elderly Rx – Comprehensive geriatric assessment Event prevented (long term nursing home admission)
= 10% in control group and 4% in experimental How large was the treatment effect?
– Risk without therapy (Baseline)= X– Risk with therapy = Y– Absolute Risk Reduction(ARR) (risk difference) = X -
Y– Relative risk reduction (RRR)=X-Y (ARR)/X
Critical Analysis of Therapy or Prevention Studies
Are the results of the study valid?
What are the results?Will the results help me in caring
for my patients?
Critical Analysis of Therapy or Prevention Studies
Will the results help me in caring for my patients?– Are the results applicable to my
patient?– Were all clinically important
outcomes considered?– Are the likely treatment benefits
worth the potential harm and costs?
Critical Analysis of Therapy or Prevention Studies
Will the results help me in caring for my patients?– Are the results applicable to my
patient?
Critical Analysis of Therapy or Prevention Studies
Will the results help me in caring for my patients?– Were all clinically important
outcomes considered?
Critical Analysis of Therapy or Prevention Studies
Will the results help me in caring for my patients?– Are the likely treatment benefits
worth the potential harm and costs (number needed to treat)?
Critical Analysis of Therapy or Prevention Studies
Number needed to treat– 1/ARR– Benefits AND risks (including costs)
of treatment depend on:–RRR–Risk of adverse outcome it is
designed to prevent (i.e., prior probability)
Critical Analysis of Therapy or Prevention Studies
Ezekowitz et al, 1992 - Warfarin Rx with nonvalvular atrial fibrillation– Baseline risk of stroke = 0.043– Risk of stroke with Rx = 0.009– ARR = 0.043-0.009 = 0.034– NNT to prevent 1 stroke = 1/0.034= 30
Critical Analysis of Therapy or Prevention Studies
Importance of baseline risk (prior probability) - Example: beta blocker after MI– Baseline risk = 0.01 vs. 0.10– RR with therapy = 0.75– ARR = ? And ?– NNT = ? And ?
Critical Analysis of Therapy or Prevention Studies
Diastolic BP 115-129– Baseline risk of death, stroke or MI =
13%– Risk of death, stroke or MI with Rx =
1.4%– NNT=
Critical Analysis of Therapy or Prevention Studies
Diastolic BP 90-109– Baseline risk of death, stroke or MI =
5.5%– Risk of death, stroke or MI with Rx =
4.7%– NNT=