Who Serves As Test Subjects?
At UMTRI, we pay special attention to the selection of test subjects. Standard practice is to test both young (30 and under) and mature drivers (65 and above) with an equal number of men and women in each age group. Increasingly, the older population is being partitioned into two age groups, 65-75, and over 75. In some cases, a middle aged group has also been examined. Drivers are recruited either from newspaper ads or from previous subject lists. Participants come from Ann Arbor, Ypsilanti, Saline, and other surrounding communities, which provides a mix of subjects from various educational, occupational, and socioeconomic groups. We usually do not sample based on income or other variables. Such factors are often irrelevant to driver performance. They result in samples that are overcontrolled and cannot be obtained at a reasonable cost. Even though Ann Arbor is a college town, it is extremely rare that only students participate in an experiment. Where special populations are sampled (e
