Fatal traffic crashes in New Zealand
Explain that removing the trend in a time series is equivalent to plotting the residuals,
ei = yi − trendi
Use this diagram to show how the time series plot of residuals is really a form of 'straightening' of the original time series.
The detrended series highlights years (or groups of years) with unusually high or low values.
The data set gives the number of fatal vehicle crashes in New Zealand per 100,000 population between 1970 and 2005.