# How can I compute the lower and upper bounds of a confidence interval in a linear regression problem?

I am completing a university statistics assignment on the Mathematica program, and this is the initial question: "The Medical Research Council wanted to evaluate the effects of different dosages of a drug that was designed to reduce pain in patients. To test this, they tested 4 levels of the drug.
The different levels were 0, 0.1, 0.2, 0.3, micrograms per milliliter. The experimenter attempted to recruit 4 patients for each level of the drug. Volunteers were randomly assigned to the different levels of the drug. After being on that dosage of drug for two weeks, patients were asked to rate their pain on a scale of 0 to 10, where 0 meant no pain at all and 10 meant that they were in excruciating pain. Pain judgments are usually normally distributed with the variance approximately independent of the mean. Pain judgements were collected in private for each patient. (Sometimes patients will drop out of a study so the number in each group is not always the target number. Analyze the data. Use[Alpha] = 0.05."

This problem has an N=16, and df=14. I have computed SSX,SSY,SXY, By, Ay,SSE, Sx|y, Sb, t-obtained, Y|xp, and Sy|xp..

Now, it is asking me to compute the lower and upper boundaries of the confidence interval , and also to use an Alpha of 0.01 (different from the alpha stated above). I have the formula, it is -Talpha/2*Sy|xp, but I am not sure as to how to apply it. I have the "Sy|xp" value, but I do not know how to find the "-Talpha/2" value. If anyone could help to explain this to me, I would really appreciate it. Thank you.

• I forgot to add that Sy|xp = 0.376393
– Ana
Commented Apr 3, 2015 at 1:04
• Please add the [self-study] tag & read its wiki. Commented Apr 3, 2015 at 1:45