Certain behaviors (e.g., drug addiction or mass sociogenic illness) might propagate from person to person, but the epidemic curve will not necessarily reflect generation times. Epidemic curves for large geographic areas might not reveal the early periodicity or the characteristic increase and decrease of a propagated outbreak.
This demonstrates how review of secular trends can bring attention to key events, improvements in control, changes in policy, sociologic phenomena, or other factors that have modified the epidemiology of a disease. For certain conditions, a description by season, month, day of the week, or even time of day can be revealing.
Strictly speaking, in computing rates, the disease or health event you have counted should have been derived from the specific population used as the denominator. However, sometimes the population is unknown, costly to determine, or even inappropriate.
Disease Global Burden Eb June Simplified Image Image Diagram - Chart - diagrams and charts with labels. This diagram depicts Disease Global Burden Eb June Simplified Image Image