question on confidence interval

Question

n a test of the effectiveness of garlic for lowering​ cholesterol,

42

subjects were treated with garlic in a processed tablet form. Cholesterol levels were measured before and after the treatment. The changes

​(beforeminus−​after)

in their levels of LDL cholesterol​ (in mg/dL) have a mean of

2.9

and a standard deviation of

18.9

Construct a

99​%

confidence interval estimate of the mean net change in LDL cholesterol after the garlic treatment. What does the confidence interval suggest about the effectiveness of garlic in reducing LDL​ cholesterol?

Answer 1

In a normal distribution, 99% of data values fall within 2.58 standard deviations of the mean. A confidence interval of 99% would therefore be "mean +- 2.58 x standard deviation" which for a mean of 2.9 and a standard deviation of 18.9 would come to [-45.9, 51.7], which suggests that the effect of garlic is very slight at best, if not entirely negligible.