ABSTRACT
Any subset of the population is called a sample. e population characteristic of interest is called a parameter. Say that we are interested in the average travel time from A to B during the morning peak hour on weekdays. If we could track all vehicles traveling from A to B, we would have the entire population of travel times and could answer questions directly. Oen it is not possible to obtain the population. For this example, a sample of a number of probe vehicles traveling from A to B would be recorded. We would then use the sample data to make inferences about the population. For instance, the population mean parameter, µ (e.g., average travel time from A to B), can be estimated by the sample average travel time of the probe vehicles ( x ), and the population variance parameter, σ2, can be estimated by the sample variance ( s2 ). Note that while we can
estimate the population parameters ( μ,σ2 ) with the sample mean and variance, respectively, we have not discussed the accuracy of these estimates. Answering this type of question will be a concern in the chapters that follow.
