stat

Lab 2: Two-sample Tests

Stat 244 Spring 2015 Week 6

This lab must be done by yourself. Your name and section number MUST be typed into the Excel spread- sheet (not handwritten on the printout).

The example shown below does not use the actual data set. The real assignment is at the end.

Matched Pairs

Enter the data in two columns in Excel. The first cell in each column should be a label, with the data values beginning immediately below it. In this example, the numbers are cholesterol measurements for 12 people, taken first when they are on a cornflake diet and again when they are on an oat bran diet.

You will use the T.TEST function (which may be called TTEST in older versions of Excel). Inside the pa- rentheses, you specify the range of data indicating the first item in each pair, then the range of data for the second item in each pair, and then two more numbers. The “2” that you see in the formula above shows that you are doing a 2-sided test (and a “1” in that position would indicate a 1-sided test). The final “1” in the formula tells Excel to do a matched pairs test. The other options in that position will be discussed in the next example.

The output of the formula is the p-value for the test. In the example shown above, the p-value is 0.01118. At the 5% level of significance, we would reject the null hypothesis.

To complete the problem, you must write your null and alternative hypotheses, your decision (Reject or Fail to reject H0).

Independent Samples

Enter the data in the same manner as in the previous problem.

The only difference in Excel between conducting a matched pairs test and an independent samples t-test is the final number that appears in the T.TEST formula. For matched pairs, the final number in the formula was a “1”. For independent samples, the final number should be “3”. [Note: the formula also accepts a “2” in that position, and conducts the pooled version of the test, which we do not use in this class.]

Again, you must write your null and alternative hypotheses, your decision.

Lab 2 (due Week 6 at recitation)

Problem 1: Use the file called “ratings.xlsx”. This file contains product ratings by males and fe- males in 14 households. At the 5% level of significance, test to see if the males rate the product higher than the females do.

Problem 2: Use the file called “SAT.xlsx”. The file contains SAT math scores for 15 students in 2013 and 17 students in 2014. At the 5% level of significance, see if the data set supports the hypothe- sis that the mean score in 2014 was different than the mean score in 2013.

( Mak e sur e t o include: your null and alternative hypothes e s, in the correct for m at your decision (Reject or Fail to reject H 0 ) The above ite m s must be typed on the printed copy. Use at least four significant digits in your answers. )