The field of public health aims to improve the health of as many people as possible as rapidly as possible. Since 1900, the average life span in the United States has increased by more than 30 years; 25 years of this gain have been attributed to public health advances.(1,2) Globally, life expectancy doubled during the 20th century,(3) largely as a result of reductions in child mortality attributable to expanded immunization coverage, clean water, sanitation, and other child-survival programs.(4) Public health focuses on denominators - what proportion of all people who can benefit from an intervention actually benefit. Maximizing health requires contributions from many sectors of society, including broad social, economic, environmental, transportation, and other policies in which government plays key roles; involvement of civil society; innovation by the public and private sectors; and health care and public health action. Although there has sometimes been distrust and disrespect between the health care and public health fields, 5 they are inevitably and increasingly interdependent; maximizing potential health gains is a defining challenge for both fields.
