Hello,

I am taking a biostatistics course and have a question on the following. Since it is asking for a 95% confidence interval, I would assume that it wants to test the level at .05. However in the solution to the problem, i have to divide .05 by 2 to get .025 for the t value which is 2.00247. Can someone please explain why that is and why it will not be right keeping it at .05

A crossover study was conducted to investigate whether oat bran cereal helps to lower serum cholesterol levels in hypercholesterolemic males. Fourteen such individuals were randomly placed on a diet that included either oat bran or corn flakes; after two weeks, their low-density lipoprotein (LDL) cholesterol levels were recorded. Each man was then switched to the alternative diet. After a second two-week period, the LDL cholesterol level of each individual was again recorded. The data from this study are shown below.

a. Construct a 95% confidence interval for the population mean.