clinical study: observational study design for making epidemiological observations of the effects of different clinical treatments or exposures on comparable cohorts or selected groups of people. The most common observational study designs are cohort studies and case–control studies

clinical trial: an experimental design for directly comparing clinical effects in human participants who are allocated to groups that receive different treatments – for example, to compare a drug treatment with a placebo. The most rigorous clinical trial design is the randomised controlled trial, in which participants are randomly allocated to the treatment groups