A researcher is interested in cellphone use and driving safety. He is specifically interested in determining if there is any difference in crash risk between hands-free and hand held cell phone use. To explore this question he has participants complete a driving course while carrying on a conversation on a cell phone two times. One time using a hand held cell phone and the other time using a hands-free set up. What type of test statistic should he use to answer her research question?

• One-sample z-test
• t-test for the significance of the correlation coefficient
• t-test for dependent samples
• t-test for independent samples
• simple analysis of variance