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EBP Pyramid

Unfiltered Resources

Evidence is not always available via filtered resources. Searching the primary literature may be required. Learn more about each type of study below and the relevant databases where you can find each study type.

Randomized Controlled Trials (RCTs)

In RCTs, study participants are randomly assigned to one of two intervention groups.

  • One group, the control group, receives the control intervention. The other group receives a different assignment/intervention.
  • During a predetermined time period both groups receive follow-up treatment and observation.
  • Because the groups are similar in composition, different outcomes in the patient groups are attributed to the control intervention/treatment.

A flowchart that shows the division of participants into two groups: control and experimental groups. Each group is then observed and compared.

 

Databases

Cohort Studies

Cohort studies are a type of medical study used to investigate the causes of disease, establishing links between risk factors and health outcomes. These studies examine cohorts of people before the occurrence of certain outcomes. They study causation, so they are usually forward-looking - that is, they are "prospective" studies, or planned in advance and carried out over a future period of time. 

Cohort studies, especially prospective studies, are often also referred to as longitudinal because of the length of time it takes to observe the study population.

Flowchart displaying the process for a cohort study, where the study population is split into two groups (individuals who have been exposed to a certain risk factor and those who have not been exposed). Then, both groups are observed longitudinally to determine the rate of individuals developing a particular disease/condition.

Case Control Studies

Case Control studies serve the purpose of comparing patients with a particular disease/condition (cases) with patients who do not (controls). Researchers then look retrospectively to compare medical histories and records of both patient groups to identify potential exposures and risk factors present in each group. This seeks to determine a relationship between a given risk factor and a disease.

No intervention, treatment, or drug is administered during this study - it is purely observational. These retrospective studies are meant to estimate odds or likelihood of individuals potentially developing a condition due to exposure to a particular risk factor.

Case control studies are commonly referred to as 'retrospective studies' and 'case-referent studies' (Himmelfarb Health Sciences Library).

Flowchart depicting the process of a case control study. Two separate populations (group of interest and control group) are reviewed in terms of medical history and records independently. Records are then compared to determine any potential trends in risk factors or exposures that may have led to the group of interest developing a particular case.