3.4 Methods used by official statistics agencies
US Census Bureau, Australian Bureau of Statistics and other official statistics agencies have developed their own decomposition procedures which are used for seasonal adjustment.
3.4.1 X-11 method
It requires the seasonal package.
x11_dcmp <- us_retail_employment %>%
model(x11 = X_13ARIMA_SEATS(Employed ~ x11())) %>%
components()
autoplot(x11_dcmp) +
labs(title =
"Decomposition of total US retail employment using X-11.")+
ggthemes::theme_pander()
The X-11 trend-cycle has captured the sudden fall in the data due to the 2007–2008 global financial crisis better than either of the other two methods.
x11_dcmp %>%
ggplot(aes(x = Month)) +
geom_line(aes(y = Employed, colour = "Data")) +
geom_line(aes(y = season_adjust,
colour = "Seasonally Adjusted")) +
geom_line(aes(y = trend, colour = "Trend")) +
labs(y = "Persons (thousands)",
title = "Total employment in US retail") +
scale_colour_manual(
values = c("gray", "#0072B2", "#D55E00"),
breaks = c("Data", "Seasonally Adjusted", "Trend")
)+
ggthemes::theme_pander()
To help us visualise the variation in the seasonal component over time