1. The problem statement, all variables and given/known data A diet pill is given to 9 subjects over six weeks. The average difference in weight (follow up - baseline) is -2 pounds. What would the standard deviation have to be for the 95% T confidence interval to lie entirely below 0? ANSWER: Around 2.6 pounds or less Refer to the previous question. The interval would up being [-3.5, -0.5] pounds. What can be said about the population mean weight loss at 95% confidence? A: We can not rule out the possibility of no mean weight loss at 95% confidence. B: There is support of mean weight gain at 95% confidence. C: There is support at 95% confidence of mean weight loss. D: We can not rule out the possibility of mean weight gain at 95% confidence. 2. Relevant equations 3. The attempt at a solution I have three attempts to answer this question. On my first attempt, I said D, thinking that since 5% of intervals do not contain the population mean, there is a chance that the population mean could be positive (and there a mean weight gain). But I got the wrong answer, and I don't understand why. On my second attempt, I thought that "weight gain" wasn't necessarily going to occur but "no mean weight loss" was, so I chose A, and I still got the wrong answer. I am surprised that confidence intervals will guarantee a support (as the remaining answers of the question suggest), so I now think the answer is C. B sounds ridiculous, because it doesn't make sense why there is support for mean weight gain at 95% confidence. Can someone help me understanding the question? I hope I finally get this question right. Thank you.