synonyms: case comparison study, case history study, case Referent Study, Retrospective Study. A study that starts with the identification of persons with the disease (or other outcome variable) of interest, and a suitable control (comparison, reference) group of persons without the disease. The relationship of an attribute to the disease is examined by comparing the diseased and nondiseased with regard to how frequently the attribute is present or, if quantitative, the levels of the attribute, in each of the groups. Such a study can be called ''retrospective'' because it starts after the onset of disease and looks back to the postulated causal factors. Cases and controls in a case control study may be accumulated ''prospectively;'' that is, as each new case is diagnosed it is entered in the study. Nevertheless, such a study may still be called ''retrospective'' because it looks back from the outcome to its causes. The terms ''cases'' and ''controls'' are sometimes used to describe subjects in a randomized controlled trial but, the term ''case control study'' should not be used to describe such a study (from Last, 1988)