The article "Behavioural Effects of Mobile Telephone Use During Simulated Driving" (Ergonomics, 1995: 2536-2562) reported that for a sample of 20 experimental subjects, the sample correlation coefficient for x = age and y = time since the subject had acquired a driving license (yr) was .97. Why do you think the value of r is so close to 1? (The article's authors give an explanation.)