5. Two-Group t-Test of the Difference of the Means for Independent Groups

Up until now in this book, you have been dealing with the situation in which you have had only one group of people (or objects) in your research study and one measurement “number” on each of these people. This chapter asks you to change gears and deal with the situation in which you are measuring two groups of people instead of only one group of people. The nine steps for hypothesis-testing using the two-group t-test are presented, including the decision rule for either accepting or rejecting the null hypothesis for your data, and writing both the result and conclusion of your statistical test. Two formulas are presented in this chapter for this test. You need to use Formula #1 whenever both of your groups have more than 30 people in them, and Formula #2 whenever one or both of your groups have less than 30 people in them. The Excel steps are presented for both of these formulas using a practical example. Three practice problems are given at the end of the chapter to test your Excel skills, and the answers to these problems appear in Appendix A of this book. An additional practice problem for each chapter is presented in the Practice Test given in Appendix B along with answers in Appendix C of this book.