Skip to main content

Evidence-Based Healthcare Resources

Resources of evidence-based medicine

Levels of Evidence

Study Designs

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

Reporting Standards for Scientific or Medical Research

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