Case control study. Observational, retrospective study that investigates causes of disease by studying a group known to have the disease (case) and a group known to not have the disease (control). Case control studies start with a known outcome and trace back to investigate possible causes of that outcome.
Cohort study. Long-term, observational study that looks at large groups of people over a period of time—even several years—to try to find out what might cause a disease or to identify possible risk factors for that disease. The most common cohort studies are prospective (forward-looking) and can produce a significant amount of data. Less common are retrospective (backward-looking) studies, using data that already exists.
Cross-sectional study. Observational study where investigators examine effects and outcomes at the same time, without interfering with participants at all. Like a snapshot, this study compares different population groups at a single point in time. Researchers can compare different variables but are unable to examine cause-and-effect relationships.
Observational study. A type of clinical study in which researchers merely observe; no intervention or treatment is administered to participants and no control group is defined.
Placebo-controlled trial. A clinical trial that involves using a control group to compare the effects of a specific treatment. The control group receives a placebo, or inactive treatment.
Systematic review. A review that exhaustively summarizes the results of available studies (controlled trials) related to a specific research question. It’s often performed before a clinical trial begins.
Randomized control trial. Known as the gold standard in medical testing, randomized control trials use humans to test the safety and potential benefit of a treatment. After assigning groups randomly, these trials determine the effects of a treatment on a specific group of people while measuring against a control group that either doesn’t receive the treatment or receives an inactive treatment (placebo). Randomized control trials are an important step toward FDA approval of any treatment.
Treatment clinical trial. Treatment clinical trials are interventional trials that study the effects of a new, untested treatment on patient volunteers with a specific disease.