Question

In this section you have discussed taking samples. For this post you will plan how you will take a sample. At NCSU there are approximately 31,000 students and about 7,000 faculty and staff. We would like to compare the cars of students with those of faculty/staff. Specifically we would like to determine if the average mileage (odometer reading NOT MPG)  for students’ cars is higher than that of faculty/staff cars. To answer this question we need to collect a sample of cars from each group. In this post you should explain how you would carry out this sample. The sample should consist of 200 subjects with at least 100 subjects from each group. You should explain how you will select this sample and how you would collect the information. You should be complete but you should also be concise. Explain the important details that may be relevant. Your post should be approximately 2 to 4 paragraphs.

Answer 1

The way in which we select a sample of individuals to be research participants is critical. How we select participants (random sampling) will determine the population to which we may generalize our research findings. The procedure that we use for assigning participants to different treatment conditions (random assignment) will determine whether bias exists in our treatment groups (Are the groups equal to all known and unknown factors?)

Before a sample is taken, we must first define the population to which we want to generalize our results. For this study, we need to sample from the population at NCSU which consists of 31,000 students and 7,000 faculties and staff. The sample which needs to collect is the average mileage of their cars through odometer readings. Before a sample can be chosen randomly, it is necessary to have a complete list of the population from which to select. First, one needs to create another list of subjects from the population who rides a car that will be the final population. After a list of the population, members have been constructed, various random sampling options are available. Some common ones include tossing dice, flipping coins, spinning wheels, drawing names out of a rotating drum, using a table of random numbers, and using computer programs. Except for the last two methods, most of the techniques are slow and cumbersome. Tables of random numbers are easy to use, accessible, and truly random. A more recent method of random sampling uses the special functions of computer software.  Many of these database programs have a function for generating a series of random numbers and a function for selecting a random sample from a range of entries in the database.

Finally, we must contact each of those selected for our sample and obtain the information needed. Failing to contact all individuals in the sample can be a problem, and the representativeness of the sample can be lost at this point.  Ideally, all individuals in a sample should be contacted. As the number contacted decreases, the risk of bias and not being representative increases. In preparing our report, we would first clearly acknowledge that not all members of the sample participated and therefore the sample may not be random—that is, representative of the population.   Then we would make available to the reader or listener of our report the number of participants initially selected and the final number contacted, the number of participants cooperating, and the number not cooperating. We would attempt to assess the reason or reasons participants could not be contacted and whether differences existed between those for whom there were data and those for whom there were no data. If no obvious differences were found, we could feel a little better about the sample’s being represented. However, if any pattern of differences emerged, such as sex, education, or religious beliefs, a judgment would have to be made regarding how seriously the differences could have affected the representativeness of the sample.