A researcher, interested in the onset of early menses, compared the life experiences and history of 1000 14-year-old girls, half of whom had monthly periods and half of whom did not, to determine what variables might be observed. Which would be the most appropriate categorization of this study?

This study would be most likely classified as a retrospective study. A retrospective study is a study performed posteriori, using information or events that have already occurred, it involves the comparison of two groups of people, those who experience a certain condition or disease (presence of monthly periods) and those who do not (absence of monthly periods). There are two types of retrospective studies which are; the case-control study and the retrospective cohort study.