Todd is a research and program evaluation specialist at the Steamville Transportation. His manager tasks him with preparing an assessment of customer satisfaction with the light rail system in general, and with particular attention to satisfaction with individual station improvements. About 50,000 commuters use a monthly pass, and Todd has access to that list and has acquired permission to contact those rail users for the purposes of measuring satisfaction.

How do you think Todd should try to sample from this list? What would your approach be? Even more important, what do you think the implications are of using just the list of monthly pass rail users? Would Todd be missing someone important from the population of interest? And further, is that population of interest clearly defined?