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Nursing Research Guide

Evidence Hierarchy

Evaluating Nursing Articles - Evidence-Based Nursing Research ...

Level I Evidence 

  • Systematic Review of Randomized Controlled Trials: 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.
  • Meta-Analysis of Randomized Controlled Trials: A process of using quantitative methods to summarize the results from 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
  •  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 2 Evidence 

  • Randomized Controlled Trial (RCT): 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 3 Evidence

  •  Controlled Trial: experimental design that studies the effect of an intervention or treatment using at least two groups: one that received the intervention and one that did not; participants are NOT randomly assigned to a group.

Level 4 Evidence

  •  Cohort Study: 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). 
  • Case-Control Study: 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 5 Evidence

  •  Systematic Review of Descriptive and Qualitative Studies: See Level 1 evidence above for more information about systematic reviews.

Level 6 Evidence

  •  Single descriptive or qualitative study
    • Qualitative research: method that systematically examines a phenomenon using an inductive approach & exploration of meaning of phenomenon; purpose is to understand & describe human experience, explore meanings & patterns; data are often narrative.

Level 7 Evidence 

  • Expert opinion: Recommendations from persons with established expertise in a specific clinical area often based on clinical experience; not considered a research method because systematic (or critical) inquiry is lacking.