In health care, a<unk>  is a comparison test of a medication or other medical treatment (such as a medical device), versus a placebo (inactive look-a-like), other medications or devices, or the standard medical treatment for a patient's condition.<unk> s vary greatly in size: from a single researcher in one hospital or clinic to an international multicenter study with several hundred participating researchers on several continents. The number of patients tested can range from as few as 30 to several thousands.  While undergoing the<unk> , the agent being tested is called an investigational new drug.
In a<unk> , the investigator first identifies the medication or device to be tested. Then the investigator decides what to compare it with (one or more existing treatments or a placebo), and what kind of patients might benefit from the medication/device. If the investigator cannot obtain enough patients with this specific disease or condition at his or her own location, then he or she assembles investigators at other locations who can obtain the same kind of patients to receive the treatment. During the<unk> , the investigators: recruit patients with the predetermined characteristics, administer the treatment(s), and collect data on the patients' health for a defined time period. (These data include things like vital signs, amount of study drug in the blood, and whether the patient's health gets better or not.) The researchers send the data to the<unk>  sponsor, who then analyzes the pooled data using statistical tests.
Some examples of what a<unk>  may be designed to do:
assess the safety and effectiveness of a new medication or device on a specific kind of patient (e.g., patients who have been diagnosed with Alzheimer's disease for less than one year)
assess the safety and effectiveness of a different dose of a medication than is commonly used (e.g., 10 mg dose instead of 5 mg dose)
assess the safety and effectiveness of an already marketed medication or device on a new kind of patient (who is not yet approved by regulatory authorities to be given the medication or device)
assess whether the new medication or device is more effective for the patient's condition than the already used, standard medication or device ("the gold standard" or "standard therapy")
compare the effectiveness in patients with a specific disease of two or more already approved or common interventions for that disease (e.g., Device A vs. Device B, Therapy A vs. Therapy B)
Note that while most<unk> s compare two medications or devices, some<unk> s compare three or four medications, doses of medications, or devices against each other.
Except for very small<unk> s limited to a single location, the<unk>  design and objectives are written into a document called a<unk>  protocol. The protocol is the 'operating manual' for the<unk> , and ensures that researchers in different locations all perform the<unk>  in the same way on patients with the same characteristics. (This uniformity is designed to allow the data to be pooled.) A protocol is always used in multicenter<unk> s.
Because the researchers test hypotheses and observe what happens,<unk> s can be seen as the application of the scientific method to understanding human or animal biology.
Synonyms for<unk> s' include<unk>  studies, research protocols and medical research.
The most commonly performed<unk> s evaluate new drugs, medical devices (like a new catheter), biologics, psychological therapies, or other interventions.<unk> s may be required before the national regulatory authority will approve marketing of the drug or device, or a new dose of the drug, for use on patients.
Clinical trial
Longitudinal studies
Longitudinal study
Cohort study
Placebo-controlled studies
Randomized controlled trial
Cross-sectional study
Action study