I am teaching introductory statistics even though statistics is not really my specialty. I encourage my students to use a TI-83 calculator(even though most of them cannot afford one). However there is one statistical procedure that always comes up with a different result when I use the TESTS menu on the TI-83 versus using a t-distribution table and the formula in the textbook, namely a non-pooled t-confidence interval for the difference between two means. (Every other statistical procedure, e.g. a pooled or non-pooled t-test, or a pooled confidence interval, comes out the same when I do it either way.)
For example: x1bar = 349, x2bar = 383 (sample means), s1 = 19.6, s2= 39.5 (sample standard deviations), n1 = 10, n2 = 7 (sample sizes), find a 95% confidence interval for mu1 - mu2 (difference in population means). When I use the formula in the textbook with critical t = 2.447 (df = 6, using one less than the smaller sample size) from the table, I get 349 - 383 +/- 2.447*sqrt[19.6^2/10 + 39.5^2/7] which comes out to the interval (-73.56, 5.56). However, when I put the same information into the TI-83 (option "0" on the TESTS menu) and choose "no" for pooled, it gives me the interval (-71.21, 3.21). If I do a t-test with the same data, it comes out the same either way. What am I doing wrong? Thank you. Howard Wachtel Delaware Valley College [EMAIL PROTECTED] . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
