01/28/2020
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The following topics will be covered in this lecture:
We have begun to consider the differences between a sample and population.
The motivation of sampling is to represent the population with a smaller collection of data points, the sample.
However, if the data is not collected in methodological way, it the sample may grossly mis-represent the population.
We will now consider in detail how we can methodically choose samples, to reduce the effects of bias.
We typically have data that can be categorized into on of the two following types of data:
The differences between the two types of data can be easily seen considering a clinical trial.
An observational version of this study might take the following form:
A major difference between the types of observations is that observational studies do not have a way to control for non-measured variables that may have an effect on the study.
Discuss with a neighbor: suppose a poll is given to UNR students about the quality of UNR food services. Is this poll an observational study or an experiment?
Discuss with a neighbor: suppose UNR wants to examine student satisfaction with possible menu changes in its food services. One group of students is given the current menu, while another group is given a new menu, and the satisfaction of each student is recorded for a month. Is this study an observational study or an experiment?
We have seen that voluntary sampling is flawed because it leads to certain groups (with strong feelings about the questions) to be highly represented while other groups (who may not care) to have limited representation.
Put another way, one group has a higher probability of responding than other groups.
This is the motivation for random sampling…
Simple random sample: a simple random sample of \( n \) subjects is selected in such a way that every possible sample of the same size \( n \) has the same chance of being chosen.
Courtesy of Mario Triola, Essentials of Statistics, 5th edition
Courtesy of Mario Triola, Essentials of Statistics, 5th edition
Courtesy of Mario Triola, Essentials of Statistics, 5th edition
Discuss with a neighbor: what sampling method is being used in each of the following examples?