Q.Define Secular trend.

A time series is data arranged chronologically, i.e. recorded at successive points of time; option (b).

Definition. A time series is a set of observations of a variable recorded at successive points of time (or over successive time periods), in chronological order — for example annual production or monthly sales figures.

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A time series has four components.

The classical decomposition of a time series recognises four components: (i) secular trend, (ii) seasonal variation, (iii) cyclical varia …

Seasonal variation refers to the regular fluctuations of a time series that recur within one year (seasons, months, quarters).

Among the components of a time series, seasonal variation is the short-term, regular movement that repeats within a period of one year — caused by weather, customs, festivals, etc. (e.g. higher umbrella …

The multiplicative time-series model treats the observed value as the product of Trend ($T$), Seasonal ($S$), Cyclical ($C$) and Irregular ($I$) components: $y = T \times S \times C \times I$.

Reasoning. A time series has four components — Trend $T$, Seasonal $S$, Cyclical $C$, and Irregular $I$. There are two standard models:

• Additive model: $y = T + S + C + I$ (used when components are independent of the trend level). …