In Western Australia, handheld cell phone use while driving has been banned since 2001, but hands-free devices are legal. A study (published in the British Medical Journal in 2005) of 456 drivers in Perth who had been in a crash observed if they were using a cell phone before the crash and if they were using a cell phone during an earlier period when no accident occurred. Thus, each driver served as his or her own control group in the study.
a. In comparing rates of cell phone use before the crash and the earlier accident-free period, should we use methods for independent samples or for dependent samples? Explain.
b. Identify a test you can use to see whether the proportion of drivers using a cell phone differs between the period before the crash and the earlier accident-free period.