Critical appraisal

Critical Appraisalof Medical Research

Susan Fowler, MLIS314-362-8092

[email protected]

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Agenda• Study Design• PICO(T)• Types of Questions• FRISBE• Clinical Importance• 3 Therapy Examples• Resources

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Basic Study DesignsExperimental Observational• Investigator

manipulates a variable and examines effect on an outcome

• Designs – randomized controlled

trial– Controlled clinical trial

• Investigator observes outcome of naturally occurring difference in a variable

• Designs– Cohort study– Case control study– Case series study

Systematic Review Workshop ©HSLS – University of Pittsburgh

Study Designs Defined meta-analysis: a quantitative approach in which individual study findings addressing a

common problem are statistically integrated and analyzed to determine the effectiveness of interventions.

systematic review: a process by which a body of literature is reviewed and assessed using systematic methods which are intended to reduce bias in the review process and improve understandability. A controlled clinical trial in which the study groups are created through randomization.

randomized controlled trial: an experiment in which investigators randomly allocate participants into (eg treatment and control) groups to receive or not to receive one or more interventions that are being compared.

controlled clinical trial: any study which compares two groups by virtue of different therapies or exposures.

cohort study: an observational study in which a cohort is followed over time.case-control studies: retrospective research design that compares individuals with a

specific condition to those without it.case report: a detailed report of the symptoms, signs, diagnosis, treatment, and follow-

up of an individual patient. case series: a report on a series of patients with an outcome or condition of interest.

Susan Fowler, MLIS Washington University in St. Louis 2012

PICO (T)• Patient or problem - How would I describe a group of

patients similar to mine?• Intervention - Which main intervention, prognostic

factor, or exposure am I considering?• Comparison (if appropriate)- What is the main

alternative to compare with the intervention?• Outcome - What can I hope to accomplish, measure,

improve or affect?• Type of Study – Based on my question, what type of

study will provide the best answer?


Types of Questions

Type of Question Ideal Type of StudyTherapy RCTPrevention RCT > Cohort > Case ControlDiagnosis Prospective, blind controlled

comparison to gold standardPrognosis Cohort > Case Control > Case

Series/Case ReportEtiology/Harm RCT > Cohort > Case Control


*FRISBE•Follow Up•Randomization•Intention to Treat•Similar Baseline•Blinding•Equal Treatment

*Mnemonic tool created by Connie Schardt, AHIP


Follow Up – Were all patients who entered the trial properly accounted for and attributed at its conclusion?

Randomization - Was the allocation (assignment) of patients to treatment randomized?Was the allocation concealed?

Intention-to-Treat Analysis - Were patients analyzed in the groups to which they wererandomized? Were all randomized patientdata analyzed?

Similar Baseline Characteristics of Patients - Were groups similar at the start of the trial?

Blinding - Were patients, health workers, and study personnel "blind" to treatment?

Equal Treatment - Aside from the experimentalintervention, were the groupstreated equally?

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Clinical Importance

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EER (Experimental Event Rate): The proportion of patients in the experimental treatment group who are observed to experience the outcome of interest.

CER (Control Event Rate): The proportion of patients in the control group observed to experience the outcome of interest.

ARR (Absolute Risk Reduction): The absolute arithmetic difference in rates of bad outcomes between experimental and control participants in a trial. (Also referred to as risk difference).

RRR (Relative Risk Reduction): The proportional reduction in rates of bad outcomes between experimental and control participants in a trial.

NNT (Number Needed to Treat): The number of patients who need to be treated with the specified intervention to prevent one bad outcome or to produce one good outcome over the period of time specified in the study.


Outcome Present

Outcome Absent

Treated Exposed

a= b= EER a a+b

Control/not exposed

c= d= CER cc+d

RRR ARR NNT

CER EER (CER-EER) CER

CER-EER 1 ARR



Evidence at Becker (How To): http://beckerguides.wustl.edu/ebm

Duke University Evidence-Based Practice: http://guides.mclibrary.duke.edu/ebm

Centre for Evidence Based Medicine: http://www.cebm.net/index.aspx?o=1023

Library Resources

Susan Fowler, [email protected]

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QuestIons?

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Critical appraisal