Q.Classify each of the following as an example of a secular trend, seasonal variation, cyclical variation or irregular variation:

Match each situation to the component whose defining feature it shows — long-term direction, within-a-year repetition, multi-year waves, or one-off chance.

A fifty-year rise is a long-term movement; a monsoon peak repeats within each year; a sudden strike is a one-off chance event; boom-and-slump over several years is the business cycle.

We identify each component by its defining feature.

1. Steady rise in population over fifty years. This is a smooth, long-term movement in one general direction over a long period — the definition of the secular trend ($T$).
2. Jump in umbrella sales every monsoon. This fluctuation repeats every year and completes itself within a year, tied to a season — it is seasonal variation ($S$).
3. Fall in output due to a sudden two-week strike. A strike is an unpredictable, non-recurring chance event that follows no pattern — this is irregular (random) variation ($I$).
4. Boom-and-slump over four to seven years. These wave-like swings span more than one year and correspond to the business cycle of prosperity and recession, with no fixed length — this is cyclical variation ($C$).
   ✓Final answer

   (i) Secular trend; (ii) Seasonal variation; (iii) Irregular variation; (iv) Cyclical variation.

Confusing seasonal with cyclical variation. The test is the period: seasonal variation completes within one year and is of fixed length, while a cyclical swing lasts more than a year and its length varies from one cycle to the next.