In a letter to the prestigious New England Journal of Medicine, a doctor reported that 20 of his male patients with creases in their earlobes had many of the risk factors (such as high cholesterol levels, high blood pressure, and heavy cigarette usage) associated with heart disease [24]. For instance, the average cholesterol level for his patients with noticeable earlobe creases was 257 (mg per 100 mL), compared to an average of 215 with a standard deviation of 10 for healthy middle-aged men.

If these 20 patients were a random sample from a population with a mean of 215 and a standard deviation of 10, what is the probability their average cholesterol level would be 257 or higher? Explain why these 20 patients may not be a random sample.