Definition: A carefully conducted research study that compares the effects of drugs, treatments, or diagnostic tests.
For example, in a randomized controlled clinical trial to understand whether calcium tablets work to prevent broken bones in women with low bone density, women with low bone density in one group are randomly assigned to receive calcium and women with low bone density in another group are randomly assigned to the control group and receive a placebo (inactive substance). The numbers of women who suffer fractures in each group are compared to find out whether calcium works.
Definition: A clinical research study in which people who presently have a certain condition or receive a particular treatment are followed over time and compared with another group of people who are not affected by the condition.
Example: For example, the Women’s Health Initiative is a cohort study that collects information from a group of older women who are followed over several years.
Controlled Clinical Trial
Definition: A type of clinical trial comparing the effectiveness of one medication or treatment with the effectiveness of another medication or treatment. In many controlled trials, the other treatment is a placebo (inactive substance) and is considered the "control."
Example: An example of a controlled clinical trial is one in which people who took glucosamine were compared with people who did not take glucosamine to determine its effectiveness in relieving pain and improving function for people with osteoarthritis.
Definition: A way of combining data from many different research studies. A meta-analysis is a statistical process that combines the findings from individual studies.
Example: For example, researchers wanted to know about the risk of stomach bleeding in people taking aspirin. They did a meta-analysis of data from 24 clinical trials with nearly 66,000 participants and found that the risk of stomach bleeding was 2.47 percent with aspirin compared to 1.42 percent with placebo (inactive substance).
Randomized Controlled Trial
Definition: A controlled clinical trial that randomly (by chance) assigns participants to two or more groups. There are various methods to randomize study participants to their groups.
Example: An example is a randomized controlled trial (RCT) to understand whether calcium tablets work to prevent broken bones in women with low bone density. Women with low bone density are randomly assigned to one of two groups. One group receives calcium and the control group receives a placebo (inactive substance). The numbers of women who suffer fractures in each group are compared to find out whether calcium works.
Definition: A summary of the clinical literature. A systematic review is a critical assessment and evaluation of all research studies that address a particular clinical issue. The researchers use an organized method of locating, assembling, and evaluating a body of literature on a particular topic using a set of specific criteria. A systematic review typically includes a description of the findings of the collection of research studies. The systematic review may also include a quantitative pooling of data, called a meta-analysis.
Example: Scientists collected all the published studies that compared types of treatment for prostate cancer that had not spread beyond the prostate gland. They compiled the results of these studies in a comparative effectiveness review, which is a type of systematic review.
Glossary Terms. Agency for Healthcare Research and Quality. Accessed 9/2/2014: http://effectivehealthcare.ahrq.gov/glossary-of-terms/?pageaction=showterm&termid=100