validity

• • Be conducted over long period of time
• • Study very large sample sizes
• • Collect range of relevant data from a large group of both affected and unaffected people e.g age gender diet occupation lifestyle exercise habits 
• • Use control groups who are not exposed to the potential cause of disease but are similar in all other respects to the test group
• • Collect data on incidence, prevalence and mortality rates of the disease
• • Identify a possible cause of the disease and any risk factors
• • Develop a management plan with strategies to control or prevent the disease
• • Evaluate the effectiveness of control treatment or prevention programs