Samples and Populations

A population study involves examining the entire population that have a particular set of characteristics that are of interest to the researcher. Studies where the total population is examined involve a relatively small group with characteristics that are not very common, for example employees of a specific organization, or parishioners of the local church. A key feature of a population study is ensuring that EVERYONE in the target population is studied, thus lending itself to research studies involving small populations.  Population studies can become expensive as a result of the additional resources (e.g., funding, legwork, etc.) needed to conduct, therefore population studies are not feasible for all research questions, such as in instances when the target population would be very large. For example, it would be nearly impossible to survey all people who attend church all across America, or even all people who attend church in only one county in America.

An example of a research question where it would be advisable to study the entire population, as opposed to just a sample, is the effect of a professional development class on customer service performance of all 215 customer service representatives in XX Organization. The target population is all customer service representatives within that organization. A second example is studying the number of times the 500 parishoners of XX Church received spiritual counseling in a month and the effect of that counseling on their feelings of happiness. The target population is all parishioners at XX Church. Both of these examples use an entire population, rather than just a subset of the target population.

Using the populations described above, to move this research to a sample study by analyzing our variables in a subset of the target population, we could look at the effect of a professional development course on customer service performance of 75 customer service representatives chosen randomly from the entire population of the customer service representatives in XX Organization. Likewise, we could study the number of times a random sample of 250 parishioners at XX Church received spiritual counseling in the last three months and the effect that counseling on their feelings of happiness.

Two paths to finding out what you want to learn; it is important to know which one to use!

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Are there any research questions or specific hypotheses where it would be advisable to study the entire population, as opposed to just a sample? If so, what characterizes these situations? Which types of research questions and hypotheses lend themselves to a study of the entire population? Which types do not and why?