Final answer:
Epidemiology is the science that studies the causes and effects of health-related events in populations. Epidemiologists use various study designs, such as longitudinal studies and cohort studies, to investigate the development of diseases in healthy populations.
Step-by-step explanation:
Epidemiology is the science that studies the causes and effects of health-related events in populations. It focuses on patterns, causes, and effects of diseases in human populations and plays a crucial role in public health. Epidemiologists use various study designs, such as longitudinal studies and cohort studies, to investigate the development of diseases in healthy populations. For example, the Cancer Prevention Study-3 is a longitudinal study that aims to identify predictive risk factors associated with cancer by following participants over a period of 20 years.