A market researcher for a local grocery store is interested in determining whether women are more likely than men to buy the chocolate milk brand ChocMoo. (If so, the researcher would recommend that advertising for ChocMoo be geared more toward women.) To investigate, the researcher selects a sample of females and a sample of males from the store's customer database. The selected customers' monthly shopping trends are digitally monitored by the researcher through the use of a customer loyalty card. After six months, the percentage of shoppers who have purchased ChocMoo is compared between the two groups. (a)First choose whether the procedure described above is an observational study or a designed experiment. Then further categorize the procedure by choosing the correct type of observational study or designed experiment. Observational study Designed experiment prospective double-blind retrospective completely randomized