Basic Concepts in Psychological Research
The basis of the scientific method in all of the sciences is simply making observations in a systematic way and following rules of evidence. All scientists observe nature carefully and follow strict rules for using those observations to reach conclusions. In this chapter. we will discuss several of the most important ways in which the scientific method is used ill psychology.
Theories and Hypotheses
It is important to recognize that science deals in theories and not in .. truths." Theories are tentative explanations of facts and relationships in sciences. The knowledge that any science provides is tentative because our theories are always subject to revision. Theories are frequently revised because scientists are constantly testing them. A theory is tested by making a prediction based on that theory-cal1ed a hypothesis-and by conducting a study to see if the hypothesis is confirmed. For example. psychologist Tenie Moffitt (1993) has published an influential theory that states that youths who become juvenile delinquents before puberty engage in different kinds of crimes than individuals who do not commit any crimes until after puberty (Moffitt. 1993). I have tested a specific hypothesis based on that theory that states that juvenile delinquents who begin committing crimes during childhood are more likely to commit violent climes than are juvenile delinquents who do not commit their first clime until after puberty. My study confim1ed TelTie Moffitt's hypothesis (Lahey & others. 1998). This means that, like many other studies. my study provides additional reason for the field to continue to use Moffitt's theory. Confirming a hypothesis based on a theory does not mean that the theory is ··true.·· however. It is always possible that other studies will test Moffitt's theory and fail to support it. If this were to happen often. her theory would be either revised or abandoned.
Representativeness of Samples
In psychology. studies use human beings or nonhuman animals as the research participants. A relatively small group of participants-called the sample-is smdied in hopes of learning something that applies to every human being or animal. This means that studies are valid only if we select a sample that is representaril'e, or typical of all humans or animals. For example. suppose a psychologist wanted to test the hypothesis that people who are happy in their work tend to be happy in their man'iages. If that psychologist worked in a marital therapy clinic, he or she might be tempted to use the clinic' s clients as the sample. Because many people come to the clinic, it would be convenient to ask them to complete some questionnaires about their happiness at work and in marriage. People who seek help for marital problems are hardly representative of all married persons. howeyer. Using such an unrepresentati ve sample could lead to a very biased and misleading test of the hypothesis.
Psychologists have not always used representative samples in their research. Unfortunately, psychologists have too often used samples that contained too few women, too few persons of color. and too few persons of lower income and social status to be representative. This is partly because they have too frequently used college students as research participants. There is nothing wrong with college students, but they are not representative of the general population of adults in North America. On the average, they are younger and more intelligent and atypical in many other ways. It is only in recent years that psychologists have begun to use more representative samples.
Importance of Replication in Research
I were to tell you that a hypothesis had been confirmed by five studies. Would you be more convinced that it is a sound hypothesis than if it had been confirmed by only one study? Researchers also are infJuenced by the repJicatjon of the findings in many separate experiments. Indeed, the replication of formal experiments by other researchers is an es"ntial principle of science. You should doubt every finding until it has been replicated.
