Classification of Studies
Hierarchy and Classification of Research Studies
| Primary Reports | Secondary Reports | ||
A | Randomized Controlled Trial Cluster Randomized Trial Randomized Crossover Trial |
M | Meta-analysis or Systematic review Decision analysis Cost-benefit analysis Cost-effectiveness study |
| B | Prospective Cohort Study Retrospective Cohort Study | ||
| C | Non-Randomized Controlled Trial Non-Randomized Crossover Trial Case-Control Study Time Series Study Diagnostic, Validity or Reliability Study | R | Narrative review (Review article) Consensus statement Consensus report |
| D | Non-Controlled Trial Case Study or Case Series Other Descriptive Study Cross-Sectional Study Trend Study Before-After Study | X | Medical opinion |