A new drug with in vitro activity against HIV is tested on a population of patients with Western-blot confirmed HIV infections, in Mumbai. Out of the 200 individuals in the patient population, 100 individuals are chosen by a lot to receive the drug. The drug, which is tasteless, is administered in a cup of orange juice; the other patients receive pure orange juice. Neither the nurses, doctors, nor patients know which patients receive the drug. At the end of the study period, the number of CD4+ T cells is determined for all of the subjects. What is the research method used in this study?

This study conducted in Mumbai is an example of a placebo-controlled, double-blind randomized clinical trial. In this type of study, subjects with a paicular disorder are randomized (the lottery) to receive either the treatment in question or a placebo. The information about whether the patient receives the treatment or the placebo is not known to either the subject or the investigator (double-blind). This type of study may be used to infer causality, i.e., if the patients taking the medication have more CD4+ T cells than the other group, it is due to the drug in question. A case-control study (Choice : Case-control study) is a retrospective study that pairs known cases of a disease with matched controls. This type of study gives information about the impoance of risk factors. The lack of a prospective design makes inferences about causality difficult. A case repo (Choice : Case repo) is a published repo of a single incidence of a disease in a subject. This is usually done for rare diseases, or for rare associations of a disease with a paicular risk factor. A coho study (Choice : Coho study) is an observational (non-interventional) study that tracks subjects prospectively. This type of study gives a measure of incidence of a disease.