Very brief chapter overview In Chapter 1, you learned about the scientific attitude, a key aspect of which is asking questions.
In this chapter, you will learn what types of questions to ask. Specifically, you learn about four questions to ask of any study:
The rest of this course will be devoted to refining your skill at asking and answering questions about these four 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. (Studies that are not experiments can only establish correlation--and one of the most repeated phrases in all of science is "correlation is not causation.")
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 in survey research is to have a large, random, representative sample of participants. Random sampling from a population helps you to generalize your results to that larger population. Note that sample size (unless you sample is almost the entire population) has little to do with external validity: You could have a sample of a million people, but if they are not representative of your population, your large sample size would not help your external validity.
If your research question involves measuring or manipulating some state of mind (hunger, stress, fear, motivation, love, etc.), you need construct validity. As figures 2.2 (p.50) and 2.3 (p. 52) illustrate, achieving construct validity is not easy. On the contrary, establishing construct validity is the hardest type of validity to establish. Because establishing construct validity is so difficult, for much of psychology's existence, many psychologists have argued that psychology should avoid mental states entirely and focus only on observable stimuli and on observable behaviors.
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 levels 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.
