Very brief chapter overview This chapter introduces you to this course's four core concepts:
At one level, there are two basic problems about doing research to get answers to questions about human behavior.
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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