In a study of the effectiveness of garlic for lowering cholesterol, 17 subjects were treated with garlicin, which is garlic in a processed tablet form. the measurement of interest is the change in ldl level. in the sample of 17 subjects, the sample mean was 3.205 with a sample standard deviation equal of 8.600. assume all conditions are met to calculate a confidence interval from this data set.

(a) find a 90% confidence interval for the average change in the ldl level. give your answer to 3 decimal places.
( [incorrect: your answer is incorrect.] , [incorrect: your answer is incorrect.] )

(b) suppose that the conditions are not met. why shouldn't we calculate a 90% confidence interval using this data set using the usual formala?
the actual confidence level might not be 90%. as long as the sample size is over 30, then the conditions will be met so we should just repeat the study with a sample size of at least 30. if we were to sample repeatedly and calculate a 90% confidence interval from each sample, then the percent of confidence intervals that capture the average change in the ldl level might not be 90%. there is no problem with calculating a 90% confidence interval from the data as long as we use the t tables. we would not capture the sample mean 90% of the time.