A trial conducted at several geographical sites. Clinical trials are research studies involving people who use healthcare services. They often compare a new or different treatment with the best treatment currently available. This is to test whether the new or different treatment is safe, effective and any better than what is currently used. No matter how promising a new treatment may appear during tests in a laboratory, it must go through clinical trials before its benefits and risks can really be known. More are sometimes conducted among several collaborating institutions, rather than at a single institution – particularly when very large numbers of participants are needed.