C

Incidence counts only the appearance of new cases in a population during a specified period; it falls when effective preventive programmes or vaccines stop people from getting the disease but is unaffected by how well we treat patients who are already ill. Therefore, improved or newer treatment modalities change prevalence (by shortening or lengthening disease duration) rather than incidence, making statement C false, while the other statements correctly describe factors that influence or define incidence [Friedman, 1976, PMID 1259307; Tripepi et al., 2012, PMID 22842830].