1. Water fluoridation. A study looked at the number of cavity-free children per 100 in 16 North American cities BEFORE and AFTER public water fluoridation projects. The table below lists the data. You will need to manually type the data into StatCrunch to use that tool to calculate the requested information.

a)Calculate delta values (After - Before) for each city. Then construct a stemplot or boxplot of these differences. Interpret your plot.

b)What percentage of cities showed an improvement in their cavity-free rate?

c)Estimate the mean change with 95% confidence (i.e. compute a 95% CI for the mean difference).

After

Before

Delta

49.2

18.2

31

30

21.9

8.1

16

5.2

10.8

47.8

20.4

27.4

3.4

2.8

0.6

16.8

21

-4.2

10.7

11.3

-0.6

5.7

6.1

-0.4

23

25

-2

17

13

4

79

76

3

66

59

7

46.8

25.6

21.2

84.9

50.4

34.5

65.2

41.2

24

52

21

31

Stemplot of Delta Values

-0 0024

003478

10

2147

3114

No outliers spread is from -4.2 to 34.5 with a median of roughly 7.5

B. Out of 16 cities, 12 showed an improvement in their cavity-free rate: 75%

C. With a 95% confidence interval 12.21 (2.131) (3.404) = 12.21 7.25= (4.96, 19.46)

IS THIS CORRECT?