Which of the following designs will use the same subjects over a long period of time?

The design that uses the same subjects over a long period of time is typically referred to as a longitudinal study. In a longitudinal study, researchers follow the same subjects or participants for an extended period, which allows for the observation of changes over time. This type of study is beneficial in a variety of fields, including psychology, sociology, and medicine, as it provides insights into developmental changes, the long-term effects of interventions, and trends over time.

Other types of studies, such as cross-sectional studies, involve different subjects at one point in time and do not track the same individuals over an extended period. Therefore, when considering designs that involve the same subjects across time, longitudinal studies are the correct choice.