Exercise 16 of Section 12.2 gave data on and . Use the accompanying Minitab output to decide whether there is a useful linear relationship between rainfall and runoff, and then calculate a confidence interval for the true average change in runoff volume associated with a 1 m3 increase in rainfall volume.

The regression equation is rainfall Predictor Coef Stdev t-ratio P Constant 2.368 0.642 rainfall 0.82697 0.03652 22.64 0.000