Suppose that we want to test the null hypothesis that an antipollution device for cars is effective.
(a) Explain under what conditions we would commit a type I error and under what conditions we would commit a type II error.
(b) Whether an error is a type I error or a type II error depends on how we formulate the null hypothesis. Rephrase the null hypothesis so that the type I error becomes a type II error, and vice versa.