Researchers wanted to determine whether calcium can lower the systolic blood pressure of African American men. They randomly assigned 21 men to two groups. Each member of one group took a calcium supplement for 12 weeks, and each member of the other group took a placebo during the same period. The systolic blood pressures (in mmHg) of the men before and after the 12-week period are shown in Table 19.

a. Complete the third column of Table 19 by finding the difference of the first and second columns. For example, the entry 7 was found by computing 107 - 100 = 7.
b. Complete the sixth column of Table 19 by finding the difference of the fourth and fifth columns. For example, the entry -1 was found by computing 123 - 124 = -1.
c. Compute the mean of the differences in the third column. What does it mean in this situation?
d. Compute the mean of the differences in the sixth column. What does it mean in this situation?
e. Did calcium tend to lower the systolic blood pressure of individuals in the treatment group?

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Table 19 Levels of Systolic Blood Pressure in 21 African American Men Systolic Blood Pressure (mmHg) Placebo Group Calcium Group Before After Difference Before AfterDifference 124 97 113 105 95 123 109 100 114 105 112 115 116 106 102 125 104 107 110 123 102 98 114 119 114 114 121 118 107 110 136 102 130