Fatal traffic crashes in New Zealand
Use this diagram to show that high-degree polynomials can be used to provide a smooth description of a nonlinear trend, but should not be used for forecasting.
Increase the order of the polynomial, firstly focusing on its behaviour between 1970 and 2005. All polynomials displayed are least squares fits.
Repeat, but focusing on the forecasts beyond 2005. Show that the forecasts depend strongly on the degree of the model.
Warn against using polynomial models of degree 3 or higher for forecasting.
The data set gives the number of fatal vehicle crashes in New Zealand per 100,000 population between 1970 and 2005.