A study was conducted to investigate whether oat bran cereal helps to lower serum cholesterol in men with high cholesterol levels. Fourteen men were placed randomly on a diet that included either oat bran or cornflakes; after two weeks, their low-density lipoprotein (LDL) choles- terol levels were recorded. Each man was then switched to the alternative diet. After a second two-week period, the LDL cholesterol level of each person was recorded again. The data are shown in Table E2.18. Calculate the LDL difference (cornflake-oat bran) for each of the 14 men, then the mean x, variance s2, and standard deviation s for this sample of differences.

LDL (mmol/L)

Subject                         Cornflakes                          Oat Bran

1                                       4.61                                   3.84

2                                       6.42                                   5.57

3                                       5.40                                   5.85

4                                       4.54                                   4.80

5                                       3.98                                   3.68

6                                       3.82                                   2.96

7                                       5.01                                   4.41

8                                       4.34                                   3.72

9                                       3.80                                   3.49

10                                       4.56                                   3.84

11                                       5.35                                   5.26

12                                       3.89                                   3.73

13                                       2.25                                   1.84

14                                       4.24                                   4.14