ABSTRACT
INTRODUCTION In the previous chapter, we considered how we might obtain a confi - dence interval for the mean fl uoride concentration in a public water supply. As hinted in Example 9.2, there may well be a particular mean value of interest (such as the target mean of 1 ppm fl uoride for the water company). This prior idea about the population, which should be stated before the data are collected, is called the null hypothesis. Concentration values obtained from water samples by the laboratory are then compared with the claim that has been made about the true mean fl uoride level in a process known as testing the null hypothesis.
