EXAMPLE 6.1 Total Sleep Time of College Students

A recent survey describes the distribution of total sleep time per night among college students as approximately Normal with a mean of 6.78 hours and standard deviation of 1.24 hours.¹ Suppose that we select a college student at random and obtain his or her sleep time. This result is a random variable because, prior to the random sampling, we don’t know the sleep time. We do know, however, that in repeated sampling will have the same approximate (6.78,1.24) distribution that describes the pattern of sleep time in the entire population. We call (6.78,1.24) the population distribution.