Tools for Critically Appraising the Literature

Type of Question/Type of Study

Therapy — how to select treatments for patients that do more good than harm and that are worth the efforts and costs of using them.

Diagnosis — how to select and interpret diagnostic tests, in order to confirm or exclude a diagnosis, based on considering their precision, accuracy, acceptability, expense, safety, etc.

Prognosis — how to estimate our patient's likely clinical course over time and anticipate likely complications of the disorder.

Etiology — how to identify causes for disease

* Adapted from Sackett et al. Evidence-Based Medicine: How to Practice and Teach EBM (London: Churchill Livingstone, 2000): 19.

Type of Study/Study Design

Randomized Controlled Trial RCT)

A true experiment, (one that delivers an intervention or treatment), the strongest design to support cause and effect relationship, in which subjects are randomly assigned to control and experimental groups.

Cohort Study

A prospective longitudinal study that begins with the gathering of two groups of patients (the cohorts), one that received the exposure (e.g., to a disease) and one that does not, and then following these groups over time to measure the development of different outcomes (diseases).

Case Study

An intensive investigation of a case involving a person or small group of persons, an issue, or an event.

Case-Control Study

A type of research that retrospectively compares characteristics of an individual who has a certain condition with one who does not; often conducted for the purpose of identifying variables that might predict the condition.

 Question about
Look for this type of study
 THERAPY
Randomized Controlled Trial (RCT)
 DIAGNOSIS
RCT or other Controlled Trial
 PROGNOSIS
Cohort Studies, Case-Control Studies, Case Studies
 ETIOLOGY
Cohort Studies
   

* Adapted from Sackett et al. Evidence-Based Medicine: How to Practice and Teach EBM. London: Churchill Livingstone, 2000:19.

Rating System for the Hierarchy of Evidence/Levels of Evidence
Level I
Evidence for a systematic review or meta-analysis of all relevant RCTs or evidence-based clinical practice guidelines based on systematic reviews of RCTs.
Level II
Evidence obtained from at least one well-designed RCT
Level III
 Evidence obtained from one well-designed controlled trials without Randomization
Level IV
Evidence from well-designed case-control and cohort studies
Level V
Evidence from systematic reviews of descriptive or qualitative study
Level VI
Evidence from single descriptive or qualities study
Level VII
 Evidence from the opinion of authorities and/or reports of expert committees
   

* Table from Melnyk, Bernadette Mazurek and Ellen Fineout-Overholt. Evidence-based practice in nursing and healthcare. Philadelphia : Lippincott Williams & Wilkins, 2005:10.