Skip to Main Content

Types and Levels of Evidence for Nutrition/Dietetic Research

Describes different types of evidence and provides strategies for finding specific types of articles for Nutrition students

Common Study Types Definitions

This page will provide you with definitions of common article types.

Systematic Reviews

Summarize the results of a systematic literature search on a specific clinical question to develop clinical recommendations. The studies are reviewed, assessed, and the results are summarized according to the predetermined criteria of the review question. They assess the methodology, sample size, and quality of the studies, utilizing the highest-quality data available to answer specific clinical questions and develop practice recommendations.

Meta-Analysis

Takes this process one step further, reviewing a clinical question for which multiple systematic reviews exist and combining all the results using accepted statistical methodology  

Randomized, Controlled Clinical Trial

A prospective, analytical, experimental study using primary data generated in the clinical environment. Individuals who are similar at the beginning are randomly allocated to two or more groups (treatment and control) and the outcomes of the groups are compared after sufficient follow-up time.

A study that shows the efficacy of a diagnostic test is called a prospective, blind comparison to a gold standard study. This is a controlled trial that looks at patients with varying degrees of an illness and administers both diagnostic tests -- the test under investigation and the "gold standard" test -- to all of the patients in the study.

Cohort Studies

Identify a large population who already has a specific exposure or treatment, follow them over time (prospective), and compare outcomes with another group that has not been affected by the exposure or treatment being studied. Cohort studies are observational and not as reliable as randomized controlled studies, since the two groups may differ in ways other than in the variable under study.

Case Control Studies

 These are studies in which patients who already have a specific condition or outcome are compared with people who do not. Researchers look back in time (retrospective) to identify possible exposures. They often rely on medical records and patient recall for data collection. These types of studies are often less reliable than randomized controlled trials and cohort studies because showing a statistical relationship does not mean than one factor necessarily caused the other.

Case Series and 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 no statistical validity.

Background Information / Expert Opinion

Use varied evidence to present information that ranges from expert opinion to providing summaries of well-known information with established evidence. They are good resources to begin understanding a topic, learning definitions, and clinical parameters. However, when answering an EBP question, look for information with statistically significant data from resources higher-up in the pyramid.

Attribution

This page was remixed from  Adelphi University.

This work by Adelphi University is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.