Disease which shows changes in occurrence (of disease) over a long period of time: March 2013 (a, h)
Ans. B i.e. Secular trend Time trends 1. Secular (long-term) trends: Graphing the annual cases or rate of a disease over a period of years (Decades or centuries) shows long-term or secular trends in the occurrence of the disease. We commonly use these trends to suggest or predict the future incidence of a disease. Secular is influenced by population features e.g. - Change of degree of susceptibility e.g. by immunization - Socioeconomic - Environmental sanitation and - Nutritional status of a population. 2. Periodic (cyclic variation) Where disease occurrence for a period then increase again in cyclic pattern e.g. measles in prevaccination era occur every 2 - 3 years. 3. Seasonality By graphing the occurrence of a disease by week or month over the course of a year or more we can show its seasonal pattern. Example: the number of repoed cases of influenza typically increases in winter. Others increase in summer e.g. food poisoning and diarrhea Seasonal patterns may suggest hypotheses about: - How the infection is transmitted. - What behavioral factors increase risk, and - Other possible contributors to the disease or condition. 4. Rapid fluctuation Usually occur in the form of epidemics that appear abruptly and ends abruptly either natural or due to intervention 5. Day of week and time of day: Analysis at these shoer time periods is especially impoant for : Conditions that are potentially related to occupational or environmental exposures, which may occur at regularly scheduled intervals
Cyclic trend
Secular trend
Seasonal trend
Sho term fluctuations