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A Guide for Nurses and Nursing Students: Critical Appraisal

Rating System for the Hierarchy of Evidence

Level I:  Systematic review or meta-analysis of randomized control trials (RCTs)

Level II:  RCTs

Level III:  Controlled trials without randomization (also called quasi-experimental studies)

Level IV:  Case-control and cohort study

Level V:  Systematic review of descriptive or qualitative or mixed methods studies

Level VI:  A single descriptive or qualitative study or mixed methods study

Level VII:  Experiential and non-research evidence, case reports, or case series

Level VIII: Expert opinion or evidence summaries


Adapted from the following two sources:

Fineout-Overholt, E., Melnyk, B.M., Stillwell, S.B & Williamson, K.M. (2010). Critical appraisal of the evidence: Part I. American Journal of Nursing, 110(7), 47-52.

Dang, D., & Dearholt, S. (2017). Johns Hopkins nursing evidence-based practice: model and guidelines. 3rd ed. Indianapolis, IN: Sigma Theta Tau International.

Where should I look for evidence?

Depending on your PICO question, there are some publication types you can focus on to answer your question:

Most Clinical Questions:  Meta-analysis, Systematic Reviews

Therapy:  Randomized Control Trials

Diagnosis:  Prospective, blind controlled trials compared to a gold standard

Prognosis:  Cohort Study, Case Control, Case Series or Case Reports

Prevention:  Randomized Control Trials, Cohort Studies, Case Control

Etiology/Harm:  Randomized Control Trials, Cohort Study, Case Control

Cost Analysis:  Economic Analysis

Where does the Publication Type show on an indexed article?

When you are determining which category an article falls under, there are some things you should consider.  This document with screenshots offer tips for assessing the level of evidence from five different articles in PubMed.

Examples of Publication Types in PubMed

Appraisal Tools

CASP Appraisal Checklists:  This set of eight critical appraisal tools are designed to be used when reading research, these include tools for Systematic Reviews, Randomized Controlled Trials, Cohort Studies, Case Control Studies, Economic Evaluations, Diagnostic Studies, Qualitative studies and Clinical Prediction Rule.

CEBM Critical Appraisal Tools:  The Centre for Evidence-Based Medicine develops, promotes and disseminates better evidence for healthcare.  View critical appraisal worksheets for systematic reviews, diagnostics, prognosis, RCTs, & qualitative studies in multiple different languages.

Critical Appraisal Checklists: Provided by Dartmouth University.

JBI Critical Appraisal Tools:  Critical Appraisal Tools from the Joanna Briggs Institute.  This includes checklists for 12 different studies including Case Studies, Case Series, Cohort Studies, Diagnostic Test Accuracy Studies, Economic Evaluations, Prevalence Studies, Quasi-Experimental Studies (non-randomized experimental studies), RCTs, Systematic Reviews, Text and Opinion, Analytical Cross Sectional Studies, & Qualitative Research.

PRISMA Checklist:  The PRISMA 2020 statement comprises a 27-item checklist addressing the introduction, methods, results and discussion sections of a systematic review report.

Hierarchy of Evidence Definitions

Systematic Review:  A summary of evidence, typically conducted by an expert or expert panel on a particular topic, that uses a rigorous process (to minimize bias) for identifying, appraising, and synthesizing studies to answer a specific clinical question and draw conclusions about the data gathered. (Level I)

Meta-analysis:  A process of using quantitative methods to summarize the results from the multiple studies, obtained and critically reviewed using a rigorous process (to minimize bias) for identifying, appraising, and synthesizing studies to answer a specific question and draw conclusions about the data gathered. The purpose of this process is to gain a summary statistic (i.e., a measure of a single effect) that represents the effect of the intervention across multiple studies. (Level I)

  • Both Systematic reviews and Meta-analysis are sometimes called "Reviews".

Clinical Practice Guidelines:  Systematically developed statements to assist clinicians and patients in making decisions about care; ideally, the guidelines consist of a systematic review of the literature, in conjunction with consensus of a group of expert decision makers, including administrators, policy makers, clinicians, and consumers who consider the evidence and make recommendations. (Level I)

Randomized Controlled Trials (RCTs):  A true experiment (i.e. one that delivers an intervention or treatment in which subjects are randomly assigned to control and experimental groups); the strongest design to support cause-and-effect relationships. (Level II)

Quasi-experiments:  A type of experimental design that tests the effects of an intervention or treatment but lacks one or more characteristics of a true experiment (e.g., random assignment; a control or comparison group). (Level III)

Cohort Studies:  A 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 (prospective) to measure the development of different outcomes (diseases). (Level IV)

Case-control Studies:  A type of research that retrospectively compares characteristics of an individual who has a certain condition (e.g. hypertension) with one who does not (i.e., a matched control or similar person without hypertension); often conducted for the purpose of identifying variables that might predict the condition (e.g., stressful lifestyle, sodium intake). (Level IV)

Cross-sectional Studies:  A study designed to observe an outcome or variable at a single point in time, usually for the purpose of inferring trends over time. (These do not have a designated level as these are "a moment in time" and used in many different study designs).

Meta-synthesis:  A rigorous process of analyzing findings across qualitative studies. The results address a specific research question and are obtained through the synthesis of qualitative studies. The process allows researchers to find greater meaning through interpreting the qualitative data. (Level V)

Descriptive Studies:  Those studies that are conducted for the purpose of describing the characteristics of certain phenomena or selected variables. (Level VI)

Qualitative Studies:  Research that involves the collection of data in non-numeric form, such as personal interviews, usually with the intention of describing a phenomenon. (Level VI)

Case Reports/Series:  Reports that describe the history of a single patient, or a small group of patients, usually in the form of a story. (Level VII)

Case Study:  An intensive investigation of a case involving a person or small group of persons, an issue, or an event. (Level VII)

Experiential and non-research evidence: Literature review, quality improvement, program or financial evaluation, or case report. (Level VII)

Background Information/Expert Opinion/Evidence Summaries:  Fully referenced expert topic reviews written by recognized authorities who review the topic, synthesize the evidence, summarize key findings, and provide specific recommendations. (Level VIII)

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