9.36 Water fluoridation Fluoridated water has fluoride at a level that is effective for preventing cavities. A study determined the number of cavity-free children (NCF)

per 100 children in 16 North American cities BEFORE and AFTER public water fluoridation projects.

Let m denote the population mean of the difference between the NCF values BEFORE and AFTER public water fluoridation projects. Use a calculator or software for the following analyses:

a. Form the 16 difference scores, for instance 49.2 - 18.2 = 31 for city 1 and 52 - 21 = 31 for city 16, always taking AFTER–BEFORE. Construct a dot plot or a box plot. Describe the sample data distribution.

b. Carry out the five steps of the significance test for a mean of the difference scores, using H0: m = 0 and Ha: m • 0.

c. Discuss whether the assumptions seem valid for this example. What is the impact of using a convenience sample?

Transcribed Image Text:

AFTER BEFORE AFTER BEFORE AFTER BEFORE AFTER BEFORE 49.2 18.2 3.4 2.8 23 25 46.8 25.6 30 21.9 16.8 21 17 13 84.9 50.4 16 5.2 10.7 11.3 79 76 65.2 41.2 47.8 20.4 5.7 6.1 66 59 52 21