Chapter 2

Very brief chapter overview

This chapter introduces you to this course's four core concepts:

  1. construct validity,
  2. internal validity,
  3. external validity, and
  4. ethics

Chapter Summary

 At one level, there are two basic problems about doing research to get answers to questions about human behavior.

  1. The study you do may be unethical.
  2. The study you do may not answer the question.
At another level, there is only one problem: Is the study ethical?
According to APA"s ethical principles (which every researcher should consult before doing a study), a study is ethical if the potential benefits of the study outweigh the study's potential for harm. Thus, there are two ways to increase the chances that your study is ethical.
First, reduce the potential for harm. Following the nine guidelines in Box 2.1 (p. 59) can help reduce the potential for harm.
Second, make your study worth doing. This means
  1. Having an interesting, important research question; and
  2. Collecting data that will allow you to answer that question.
Mitchell and Jolley address point 1 (developing an interesting, important research question) in Chapter 3. But what about point 2 (collecting data that will allow you to answer your research question)? Obviously, your study should have validity. But what type of validity? The type of validity you will need will depend on your research question.

If your research question is about whether something causes a certain effect, your study must have internal validity.  Establishing internal validity is not easy (see Figure 2.1 on p. 48). Only studies that are experiments (and most studies are not experiments--see the colored table on p. 49) have internal validity.  Thus, if you want to make cause-effect statements, you should do an experiment. To do an experiment, you must have at treatment that you manipulate, and you must randomly assign participants to different types or amounts of that treatment.

Alternatively, if your research question is about what percentage of people do some behavior, you need a study that has external validity. One key to having external validity is to have a large, random, representative sample of participants. Random sampling from a population helps you to generalize your results to a larger population.

If your research question involves measuring or manipulating some state of mind (hunger, stress, fear, motivation, love, etc.), then you need construct validity. As figures 2.2 (p.50) and 2.3 (p. 52) illustrate, achieving construct validity is not easy.

Depending on the research question, you may often be interested in only one of these kinds of validity. Sometimes, you may want to have two of these kinds of validity. Rarely, however, will a study have high levls of all three types of validity.

Tip: Understanding the differences among the three types of validity takes some students a long time. To be one of the students who learns these key distinctions quickly, study Table 2-1 (p. 40) so that you can see how these types of validity relate to real life situations. Then, test your understanding by doing the student exercises and quizzes for this chapter.

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