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Classification of Studies

Hierarchy and Classification of Research Studies
Primary Reports Secondary Reports
 Randomized Controlled Trial
 Cluster Randomized Trial
 Randomized Crossover Trial
 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