In their book Introduction to Time Series Analysis and Forecasting (Wiley, 2008), Montgomery, Jennings, and Kulabci presented the data on the drowning rate for children between one and four years old per 100,000 of population in Arizona from 1970 to 2004. The data are: 19.9, 16.1, 19.5, 19.8, 21.3, 15.0, 15.5, 16.4, 18.2, 15.3, 15.6, 19.5, 14.0, 13.1, 10.5, 11.3, 12.9, 84, 9.2, 11.9, 5.8, 8.5, 7.1, 7.9, 8.0, 9.9, 8.5, 9.1.9.7, 6.2, 7.2, 8.7, 5.8, 5.7, and 5.2.

(a) Perform an appropriate graphical analysis of the data.

(b) Calculate and interpret the appropriate numerical sum- maries.

(c) Notice that the rate appears to decrease dramatically start- ing about 1990. Discuss some potential reasons why this could have happened.

(d) If there has been a real change in the drowning rate begin- ning about 1990, what impact does this have on the sum- mary statistics that you calculated in part (b)?