Case Control Study
A study that compares two groups of people: those with the disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls). Also called a retrospective study. (PubMed Health Glossary)
Clinical Trial
A type of research study that tests how well new medical approaches work in people. These studies test new methods of screening, prevention, diagnosis, or treatment of a disease. Also called clinical study. (PubMed Health Glossary)
Cohort Study
A research study that compares a particular outcome (such as lung cancer) in groups of individuals who are alike in many ways but differ by a certain characteristic (for example, female nurses who smoke compared with those who do not smoke). Cohort studies are a type of observational study. Also called longitudinal study or prospective study. (PubMed Health Glossary)
Controlled Clinical Trial
A clinical study that includes a comparison (control) group. The comparison group receives a placebo, another treatment, or no treatment at all. (NCI)
Longitudinal Study
Investigation in which data are collected from a number of people over a long period of time. (PubMed Health Glossary)
Meta-Analysis
A process that analyzes data from different studies done about the same subject. The results of a meta-analysis are usually stronger than the results of any study by itself. (PubMed Health Glossary)
Observational Study
A type of study in which individuals are observed or certain outcomes are measured. No attempt is made to affect the outcome. (PubMed Health Glossary)
Randomized Controlled Trial (RCT)
A study in which the participants are assigned by chance to separate groups; neither the researchers nor the participants can choose which group. (PubMed Health Glossary)
Systematic Review
The identification, selection, appraisal, and summary of primary studies that address a focused clinical question using methods to reduce the likelihood of bias. (JAMAevidence)