Answer:
Dr. Marcy is conducting an observational study that compares a group of people who have a specific disease to a control group of people who do not have that disease. This type of study is known as a cohort study.
Cohort studies are observational studies that follow a group of individuals over a period of time to investigate the occurrence of a particular disease or outcome of interest. In a cohort study, individuals are classified into two or more groups based on their exposure to a particular risk factor or characteristic, and their health outcomes are then compared.
In this case, the group of individuals with the specific disease constitutes the "exposed" cohort, while the control group of individuals without the disease constitutes the "unexposed" cohort. By comparing the two groups, Dr. Marcy can identify potential risk factors or causes of the disease, as well as assess the effectiveness of preventive measures or treatments.