Question

A powder diet is tested on 49 people, and a liquid diet is tested on 36 different people. Of interest is whether the liquid diet yields a higher mean weight loss than the powder diet. The powder diet group had a mean weight loss of 42 pounds with a standard deviation of 12 pounds. The liquid diet group had a mean weight loss of 45 pounds with a standard deviation of 14 pounds. Use the two-sample t-methods to construct a 95% confidence interval for difference in population means (μliquid− μpowder). Round your final answer to 1 decimal place.

These are the notes I got when I got the wrong answer.

Remember that the formula for the confidence interval is (x¯liquid−x¯powder)±(t∗smaller n−1)(s2liquidnliquid+s2powdernpowder−−−−−−−−−−−√). In this formula, make sure to use the 95% confidence level. Also, note that question is asking for a 95% confidence interval for μ_liquid− μ_powder. Finally, for the t-critical value, make sure to use the 97.5^th percentile in the qt() function in R. That is the point that the area to the left of it is 0.975 on the t distribution (with the correct degrees of freedom).

Answer 1