DS624 Homework 3

Problem 6.2

The plastics data set consists of the monthly sales (in thousands) of product A for a plastics manufacturer for five years.

  1. Plot the time series of sales of product A. Can you identify seasonal fluctuations and/or a trend-cycle?
autoplot(plastics, xlab="Time (year)", ylab = 'Monthly Sales (thousands)')

Overall there is a yearly cycle with the peak ~Q3 and the trough at ~Jan/Feb after christmas. Overall there is an increasing trend in sales, so business must bee good :)

  1. Use a classical multiplicative decomposition to calculate the trend-cycle and seasonal indices.
fit <- plastics %>% decompose(type='multiplicative')

autoplot(fit)