Meta-Analysis and Systematic Reviews are the gold-standard of clinical information. Systematic Reviews summarize the results of a systematic literature search on a specific clinical question to develop clinical recommendations. They assess the methodology, sample size, and quality of the studies, using the highest quality data available to answer specific clinical questions and develop practice recommendations. Meta-Analysis takes this process one-step further, reviewing clinical questions for which multiple Systematic Reviews exist to take into account all of their data and develop the highest level of statistical analysis.
Randomized Controlled Trials answer questions about the efficacy of different types of therapies. They are designed with two cohort groups, a test group and a control group, ideally with patients assigned randomly to each group. This allows the study to test a specific therapy against either no-therapy or a different course of treatment.
Cohort Studies are observational studies that compare a cohort already undergoing a treatment or with a specific, unique exposure to a separate cohort that is not utilizing the same treatment or exposure over a period of time. They are a very good method to track long-term health effects that it may be unethical to test as a randomized controlled trial, for instance exposure to a specific pollutant (smoking, radiation, etc). However, they tend to be very long studies, sometimes generational, and, because they are not randomized, are less reliable than a randomized controlled trial.
Case Control Studies look at a group of individuals with a specific condition and compare them to a group of people without the same condition. Unlike cohort studies, which follow groups over time, Case Control Studies take medical histories of patients and seek to draw statistical conclusions based on similarities in the medical histories of the patients with the condition that are not existent in the medical histories of the patients without the same condition. However, Case Control Studies cannot show true causation (that X in the patient's past causes the condition in the present), but suggest relationships between the past and present. While researchers often use Case Control Studies to seek causes for new conditions or previously unexamined conditions, then seek to verify the results by later completing cohort or randomized controlled trials.
Case Series/Case Reports report on the clinical case of a single patient or a series of patients. They use no control groups, though, meaning that they do not provide statistical significance. Useful for locating information on unusual disorders, for common clinical questions look for evidence from higher-up in the pyramid.
Background Information / Expert Opinion
These resources used varied evidence to present information that ranges from expert opinion to providing summaries of well-known information with established evidence. These are good resources to begin understanding a topic, learning definitions, and understanding clinical parameters. However, when answering an EBP question, looking for information with statistically significant data from resources higher-up in the pyramid.
For further visual explanations of the types of studies available, see Types of Studies.
Andrade, R. (2016). "Evidence Pyramid & Resources." Nursing LibGuide. University of Chicago Library. Retrieved from http://guides.lib.uchicago.edu/nursing.
SUNY. "Types of Studies." SUNY Downstate EBM Tutorial. Retrieved from http://library.downstate.edu/EBM2/research.htm.
(2016). "Type of Study." Introduction to Evidence-Based Practice. Retrieved from http://guides.mclibrary.duke.edu/ebmtutorial.