RETROSPECTIVE STUDY

A study that compares two groups of people: those withthe disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls). Researchers study the medical and lifestyle histories of the people in each group to learn what factors may be associated with the disease or condition. For example, one group may have been exposed to a particular substance that the other was not. Also called a case-control study. retroviral vector RNA from a virus that is used to insert genetic material into cells.