Review articles are also called background articles or summary articles. They describe the clinical significance of the problem, its prevalence, and relevant issues. They are not extensive and constitute a low level of evidence.
Evidence articles present evidence of the highest level. Systematic reviews are the highest level evidence articles as they provide an extensive review of the clinical research literature.
Meta Analysis – type of systematic review that combines (pools) the results using accepted statistical methodology as if they were from one large study.
Systematic Review – focuses on a specific clinical question and includes an extensive/explicit review of the literature to identify studies with sound methodology. Data extracted from the selected studies are combined (if possible), compared, and assessed. Conclusions are made based on results and/or the presence or absence of supporting evidence.
Randomized Controlled Trial (RCT) – prospective, analytical, experimental study using data obtained in the clinical environment. Individuals similar at the beginning are randomly allocated into treatment groups and outcomes are compared after sufficient follow-up time. A study that shows the efficacy of a diagnostic test is a prospective, blind comparison to a gold standard. This is a controlled trial that looks at individual with varying degrees of an illness and applies diagnostic tests to each individual: the test under investigation and the “gold standard” test.
Cohort Study – prospective, analytical, observational study of a population (or cohort) who had, have or will have a specific exposure or treatment of interest. The outcome of the cohort is compared to the general population or another group that has not been exposed to exposure or treatment of interest. Cohort studies are susceptible to bias because the two groups may differ in ways beyond the variable in the study.
Case-Control Study – retrospective, analytical, observational study based on secondary data in which individuals with a condition or outcome are compared with individuals who do not, but have the same risk factor. Often using medical records or patient recall, researches look back in time to identify possible exposures. Very useful for rare conditions or for risk factors with long induction. Due to potential bias, case control studies provide relatively weak empirical evidence even when properly executed.
Case Series/Case Report – anecdotal evidence. A description of a single case (or several cases), typically describing the manifestations, clinical course, and prognosis of that case. Due to the wide range of natural biologic variability in these aspects, a single case report provides little empirical evidence to the clinician. They do describe how others diagnosed and treated the condition and what the clinical outcome was.
