This page explains how clinicians determine the best evidence.
Evidence & Databases
Different databases contain different kinds of evidence. See the Databases tabs in this guide to find which databases have the evidence you need.
Levels of Evidence
Categories of evidence are conceptualized as a hierarchy, with the top levels considered the best evidence for clinical decision-making. These higher levels are considered secondary literature, which synthesizes, filters, and evaluates the primary (lower level) literature. The hierarchy can include:
- Systematic Reviews: A review of all research available on a given topic, conducted with strict methods of locating and synthesizing the research.
- Systematic Reviews with Meta-Analyses pool and summarize the data from each study included in the review.
- Critically-Appraised Topics: A critical appraisal of clinically relevant studies.
- Critically-Appraised Individual Articles: Articles that are selected and rated for clinical relevance by physicians.
- Randomized Controlled Trials: A study wherein the subjects are divided into two groups: one that received the genuine treatment, and one that receives a placebo treatment.
- Cohort Studies: A study that compares outcomes between two groups studied over a period of time.
- Case-Controlled Studies: A study that compares groups with differing outcomes with respect to their exposure to a suspected causal attribute.
- Case Series: A study that measures the outcome of a group of patients who receive the same treatment, with no control group.
- Case Reports: Reports on the treatment and outcome of a single patient.
More Resources for Levels of Evidence
Palmer College of Chiropractic is not responsible for the content of the external websites contained in this research guide. The views and opinions of the authors expressed in these external websites do not necessarily state or reflect those of Palmer College of Chiropractic.