Skip to Main Content

Levels of Evidence and Study Design: Study Design

Information on study design and levels of evidence to help you evaluate the medical, nursing and health care literature

Study Designs

Clinical Practice Guidelines

Translates research into practical application by using the best scientific evidence available, usually from systematic reviews or meta-analyses. They are created by a panel of experts who carefully analyze the evidence provided. Guidelines will change over time as new research and evidence is created. (Forrest JL, Miller SA, Miller GW, Elangovan S, Newman MG.)

Systematic Review

A compilation of similar studies to address a specific question using a detailed and comprehensive search strategy as well as a rigorous appraisal process. They summarize, appraise, and communicate the results and implications of all the research available on the question. (Melnyk BM, Fineout-Overholt E.)

Meta-Analysis

A type of systematic review that incorporates quantitative methods to compare the results from multiple studies. They can generate a more complete statistic of an intervention across multiple studies. It can create a summary statistic more precise than findings from an individual study. (Melnyk BM, Fineout-Overholt E.)

Randomized Controlled Trial

An experiment in which participants are randomly allocated to receive one of two (or more) interventions and are then followed to determine the effects of the intervention. (Patient-Centered Outcomes Research Institute. Glossary)

Controlled Clinical Trial

An experiment in which participants receive one of two (or more) interventions and are then followed to determine the effects of the intervention. 

Cohort Study

An experiment where one  group of participants are exposed to a condition that the other group of participants are not. They are then followed to determine the differences in specific outcomes from the two groups. (Melnyk BM, Fineout-Overholt E.)

Cross-sectional Study

 A study that examines the relationship between diseases (or other health-related characteristics) and other variables of interest as they exist in a defined population at a single point in time. (The Free Dictionary)

Case-control Study

A retrospective study where, over time, researchers survey a group of people with an outcome of interest and a group of people without that outcome to  determine differences between the groups that might account for why one group had the outcome of interest. (Melnyk BM, Fineout-Overholt E.)

Case Series

A series of case studies/reports in which patients were given similar treatments. They typically contain very detailed information about the individual patients. (NCI Dictionary of Cancer Terms)

Case Study

An intensive investigation of a case involving a person or persons, issue or event. (Melnyk BM, Fineout-Overholt E.)

Editorial

An article in a publication expressing the opinion of its editors or publishers. (The Free Dictionary)

Opinion

A belief or conclusion held with confidence but not substantiated by positive knowledge or proof (The Free Dictionary)

Animal Research

A laboratory experiment using animals to study the development and progression of diseases. These test the safety and efficacy of new treatments before they are tested in humans. (NCI Dictionary of Cancer Terms)

In Vitro Study

Research performed in the laboratory and outside the body.  (NCI Dictionary of Cancer Terms)

Note: This list is not exhaustive but represents the main types of study design. 

References

  • Forrest, J. L., Miller, S. A., Miller, G. W., Elangovan, S., & Newman, M. G. (2019). Evidence-based decision making. In Newman, Michael G., Takei, Henry H., Klokkevold, Perry R., & Carranza, Fermin A. (Eds.), Newman and Carranza's clinical periodontology (Thirteenth ed., pp. 1-9.e1). Elsevier.

  • Melnyk, B. M., & Fineout-Overholt, E. (2019). Evidence-based practice in nursing and healthcare: A guide to best practice (Fourth ed.). Wolters Kluwer. 

  • National Cancer Institute. (2010). Animal study. In NCI Dictionary of Cancer Terms. Retrieved October 1 2021.

  • National Cancer Institute. (2010). Case series. In NCI Dictionary of Cancer Terms. Retrieved October 1 2021.

  • National Cancer Institute. (2010). In vitro. In NCI Dictionary of Cancer Terms. Retrieved October 1, 2021.

  • OCEBM Levels of Evidence Working Group. (n.d.). CEBM Levels of Evidence Table. (Version 2) [Table]. Oxford Centre for Evidence-Based Medicine. Retrieved October 1 2021.

  • The Free Dictionary. (2011). Cross sectional study. In Segen's Medical Dictionary. Retrieved October 1 2021.

  • The Free Dictionary. (2011). Editorial. In American Heritage® Dictionary of the English Language, Fifth Edition. Retrieved October 1 2021.

  • The Free Dictionary. (2011). Opinion. In American Heritage® Dictionary of the English Language, Fifth Edition. Retrieved October 1, 2021.