Chapter 8: Basic Adjustments Using the Census X11 Method

8.1 Seasonality

8.2 Seasonal Adjustment Using Census X11

8.3 Seasonal Adjustment of US E-Commerce

8.4 Seasonal Adjustment of UK Unemployment

8.1 Seasonality

As a motivating example, consider the quarterly series of e-commerce in the US, which was also applied as an example of forecasting in Section 6.5. The series has large seasonal fluctuations: the sales in the fourth quarter are higher than in the first three quarters due to the extra activity among consumers in the period up to Christmas. See Figure 8.1. But the seasonality is not a regular feature because the spike in the fourth quarter in recent years is very pronounced but it was barely visible in the first years of the observation ...

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