(aka, Secondary Research)
Examples: position statements, clinical practice guidelines, literature reviews
(aka, Original Research or Primary Research)
Note: both of these types of articles are peer-reviewed literature. Clinical practice guidelines might not be peer-reviewed, however they are usually based on systematic reviews of peer-reviewed evidence and therefore are still considered scholarly sources. See below for more types of sources you might encounter in your research.
Chapters 5, 6, and 7 of your John Hopkins Evidence Based Practice textbook discuss searching for articles and types of evidence in more depth:
Evidence-Based Practice or Evidence-Based Medicine is the integration of best research evidence with clinical expertise and patient values. (Sackett DL, Straus SE, Richardson WS, et al. Evidence-based medicine: how to practice and teach EBM. 2nd ed. Edinburgh: Churchill Livingstone, 2000.)
Research articles found in library resources contain evidence you will use for clinical decision-making. You will find and use many types of sources as you search for evidence.
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Randomized Controlled Trials are studies in which subjects are randomly assigned to two or more groups; one group receives a particular treatment while the other receives an alternative treatment (or placebo). Patients and investigators are "blinded", that is, they do not know which patient has received which treatment. This is done in order to reduce bias.
Cohort Studies are cause-and-effect observational studies in which two or more populations are compared, often over time. These studies are not randomized.
Case Control Studies study a population of patients with a particular condition and compare it with a population that does not have the condition. It looks the exposures that those with the condition might have had that those in the other group did not.
Cross-Sectional Studies look at diseases and other factors at a particular point in time, instead of longitudinally. These are studies are descriptive only, not relational or causal. A particular type of cross-sectional study, called a Prospective, Blind Comparison to a Gold Standard, is a controlled trial that allows a research to compare a new test to the "gold standard" test to determine whether or not the new test will be useful.
Case Studies are usually single-patient cases.
Systematic Reviews are studies in which the authors ask a specific clinical question, perform a comprehensive literature search, eliminate poorly done studies, and attempt to make practice recommendations based on the well-done studies. (Note: systematic reviews are still considered original research because they contain a study design.)
Meta-Analyses are systematic reviews that combine the results of select studies into a single statistical analysis of the results.
Clinical Practice Guidelines are systematically developed statements used to assist practitioners and patients in making healthcare decisions.