In a clinical trial, individuals free from disease are randomly assigned to receive either a physical activity intervention or no intervention (the health education group). The two groups are followed for a period of time to determine if they differ. This difference in groups is typically revealed by the percent of people that develop the disease or health outcome of interest.

PROS:

�Random assignment of who does and does not receive the physical activity intervention minimizes potential biases.

�Data generated is prospective in nature and better than retrospectively obtained data which can be subject to participant recall bias.

�Just like the prospective design, a clinical trial can establish cause and effect. Investigators will be able to determine if physical inactivity lead to the disease or health outcome of interest.

CONS:

�Expensive

�Not suitable for study of physical activity interventions to prevent diseases or outcomes that take a long time to develop or are rare.

�Individuals may behavior differently if they know they are being watched.

�This study is subject to participant dropout and loss to follow-up.

�