Individual and societal health-related decisions about interventions to improve health and prevent disease are based on more than scientific evidence. Social, economic, ethical, environmental, cultural, and political factors may also be considered in implementation decisions. The effectiveness of a health-related strategy can be evaluated by comparing the frequency of the outcome in carefully selected groups of people who were and were not exposed to the strategy. Costs, trade-offs of harms and benefits, and alternative solutions must also be considered in evaluating the strategy
