The evidence-based pyramid helps researchers visualize the quality and rigor of different types of health research studies. The bottom part of the pyramid lists studies that are numerous but not as high a quality. However, the information in the studies listed in the bottom part of the pyramid are synthesized into the study types at the top of the pyramid. This also helps illustrate the interconnected nature of different study types and help visualize how each one is important to the research process.
From the bottom of the pyramid to the top we have: Background information and expert opinion; case-controlled studies and case series or reports; cohort studies; randomized controlled trials; critically appraised topics; and, finally, systematic reviews and meta-analysis.
Case-Controlled Study - A study that compares people with a specific disease or outcome of interest (cases) to people from the same population without that disease or outcome (controls), and which seeks to find associations between the outcome and prior exposure to particular risk factors. This design is particularly useful where the outcome is rare and past exposure can be reliably measured. Case-control studies are usually retrospective, but not always.
Case Series - A study reporting observations on a series of individuals, usually all receiving the same intervention, with no control group.
Case Study - A study reporting observations on a single individual.
Cohort Study - An observational study in which a defined group of people (the cohort) is followed over time. The outcomes of people in subsets of this cohort are compared, to examine people who were exposed or not exposed (or exposed at different levels) to a particular intervention or other factor of interest. A prospective cohort study assembles participants and follows them into the future. A retrospective (or historical) cohort study identifies subjects from past records and follows them from the time of those records to the present. Because subjects are not allocated by the investigator to different interventions or other exposures, adjusted analysis is usually required to minimise the influence of other factors (confounders).
Meta Analysis - The use of statistical techniques in a systematic review to integrate the results of included studies. Sometimes misused as a synonym for systematic reviews, where the review includes a meta-analysis.
Randomized Control Trial - An experiment in which two or more interventions, possibly including a control intervention or no intervention, are compared by being randomly allocated to participants. In most trials one intervention is assigned to each individual but sometimes assignment is to defined groups of individuals (for example, in a household) or interventions are assigned within individuals (for example, in different orders or to different parts of the body).
Systematic Review - A review of a clearly formulated question that uses systematic and explicit methods to identify, select, and critically appraise relevant research, and to collect and analyse data from the studies that are included in the review. Statistical methods (meta-analysis) may or may not be used to analyse and summarise the results of the included studies.
Cochrane. (2017). Glossary. Retrieved from http://community.cochrane.org/glossary
CONSORT - CONsolidated Standards Of Reporting Trials
EQUATOR Network - Enhancing the QUAlity and Transparency OF health Research
PRISMA - Preferred Reporting Items for Systematic Reviews and Meta-Analyses