Study Designs: Research is important for evidence-based practice. Yet, all research studies are not equal. Some are better than others, as depicted in the pyramid below. Use these definitions to gain insight into which study design is best suited for your topic.
Systematic Review:
- A review in which specified and appropriate methods have been used to identity, appraise, and summarize studies addressing a defined question. It can, but need not, involve meta-analysis. In clinical evidence, the term systematic review refers to a systematic review of RCTs unless stated otherwise.
Meta-analysis:
- "Meta-analysis is a quantitative, formal, epidemiological study design used to systematically assess previous research studies to derive conclusions about that body of research. Outcomes from a meta-analysis may include a more precise estimate of the effect of treatment or risk factor for disease, or other outcomes, than any individual study contributing to the pooled analysis" (Haidich, 2010).
Randomized Controlled Trial:
- In this design, participants are randomly assigned to two or more groups. One (the experimental group) receives an intervention that is being tested. Another group (the comparison or "control group") receives an alternative treatment or placebo. Randomized control trials allow for practitioners to assess of the effects of interventions.
Controlled Clinical Trial:
- During a controlled clinical trial, participants are assigned to two or more different treatment groups. Treatments are assigned by a method other than random allocation. When the method allocation is by random selection, the study is referred to as a randomized controlled trial (RCT). Non-randomized controlled trials are more likely to suffer from bias than RCTs.
Cohort Study:
- Cohort studies are non-experimental. They examine how events differ for individuals in the same group. Members of a group are referred to as "a cohort." Researchers use cohort studies to see how exposure to a suspected risk factor (e.g. smoking), tends to cause specified events (e.g. lung cancer). Prospective cohort studies are more reliable than retrospective cohort studies.
Case control study:
- A case control study examines a group of people who have experienced an event (usually an adverse event) and a group of people who have not experienced the same event. It looks at how exposure to suspect agents (usually noxious) affect us. This type of study design is most useful for trying to ascertain the cause of rare events, such as rare cancers.
Definitions are edited, but sourced from the British Medical Journal's Clinical Evidence Glossary, unless otherwise specified.
Hierarchy of Evidence
Reference:
Haidich A. B. (2010). Meta-analysis in medical research. Hippokratia, 14(Suppl 1), 29–37.
