Question: Figure 1.13 (below) is a time plot of the average price of fresh oranges each month during the decade from 1992-2002. The prices are index numbers given as percents of the average price during 1982-1984.

a) The most notable pattern is seasonal variation, regular up and down movements that occur at about the same time each year. Why should we expect the price of fresh oranges to show seasonal variation?

b) Is there a longer-term trend visible under the seasonal variation? If so, describe it.