Pratt Guides: Evidence Based Literature Searching: Types of Studies

Choosing the Correct Study Type

Thinking about the type of question will help you focus in on literature that is relevant to your PICO question. It can also help point you to an appropriate type of study.

This list is just a sampling of the types of questions. There are many more!

Question Type	Description	Example	Study Type
Diagnosis	How to select and interpret diagnostic tests	Can a sonography or abdominal computed tomography (CT) scan accurately diagnose acute appendicitis in children?	Randomized Controlled Trial (RCT) or Cohort Study
Therapy	How to select treatments to offer patients that do more good than harm and that are worth the efforts and costs of using them	What is the best treatment for school-aged children with migraines?	Randomized Controlled Trial (RCT)
Prognosis	How to estimate the patient's likely clinical course over time and anticipate likely complications of disease	What is the likelihood of relapse in a teenager diagnosed with bipolar?	Cohort Study or Case-Control
Harm/Etiology	How to identify causes for disease	Among adolescent females who are on low-dose oral contraceptives, what is the risk of developing a blood clot?	Cohort Study

Thinking about the type of study will help you build a good clinical question. Descriptions of the common study types are below.

Background/Expert Opinion: Evidence in these resources may vary from expert opinion to high levels of evidence
Case Series/ Case Reports: Consist of collections of reports on the treatment of individual patients or a report on a single patient. Because they are reports of cases and use no control groups with which to compare outcomes, they have little statistical validity.
Case Controlled Studies: A case control study starts with patients who already have the outcome and looks backwards to possible exposures.
Cohort Studies: A cohort study starts with the exposure and follows patients forward to an outcome.
Randomized Controlled Trials (RCTs): Randomly assigns the exposures and then follows patients forward to an outcome.
Critically Appraised Individual Articles [Article Synopsis]: Authors of critically-appraised individual articles evaluate and synopsize individual research studies.
Critically Appraised Topics [Evidence Synthesis]: Authors of critically-appraised topics evaluate and synthesize multiple research studies.
Systematic Reviews & Meta-Analyses: Authors of a systematic review ask a specific clinical question, perform a comprehensive literature search, eliminate the poorly done studies and attempt to make practice recommendations based on the well-done studies.