Public health focuses on protecting and improving the health of populations through prevention, policy, environmental measures and organized services. Unlike a purely clinical approach centered on treating individual patients, public health also asks why risks are distributed unevenly across communities. Clean water, vaccination, sanitation, nutrition and safer working conditions can prevent illness before medical treatment is needed. Public-health interventions may require cooperation among governments, communities and institutions. Effective policy must consider evidence as well as feasibility, equity and public trust. Question: The central idea is that public health: