At the start of this chapter, we noted the purpose of research. Research fuels explanation, which is the ultimate goal of science (Salmon, 1989). Evidence from research provides the information needed to develop, test, and improve scientific explanations. In psychology, the purpose of research is to provide information that psychologists can use in explaining the behavior and experiences of people, the workings of the mind, and the functioning of the brain. Now that we’ve learned about psychology’s data, research designs, and forms of scientific evidence, let’s see how psychologists formulate scientific explanations.

Scientists explain phenomena by developing sets of ideas known as scientific theories. What is a theory in science? A committee formed by the U.S. National Academy of Science has provided a particularly clear definition:

In everyday usage, “theory” often refers to a hunch or a speculation. When people say, “I have a theory about why that happened,” they are often drawing a conclusion based on fragmentary or inconclusive evidence.

The formal scientific definition of theory is quite different from the everyday meaning of the word. It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence.

—National Academy of Sciences (2008, p. 11)

When scientists say they have a theory, it does not mean that they’re just speculating. A scientific theory is a systematic, data-based explanation for a phenomenon or set of phenomena. When you read in this book that psychologists have a theory that, for example, self-confidence boosts personal achievement, or children’s thinking develops through a set of distinct stages, or pessimistic thinking styles cause people to become depressed, it means the psychologists have systematic explanations that are grounded in scientific evidence.

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A theory may be broad or narrow in scope. Sigmund Freud (1900, 1930), for example, developed a theory of remarkable breadth; it was meant to explain the overall structure of mind, the development of children, psychological distress and personality differences among adults, and the relation between the individual and society. In contemporary psychological science, John Anderson and his colleagues have developed a theory designed to explain perception, memory, problem solving, and the development of skills (Anderson et al., 2004). Yet often, theories are narrowly focused. For example, one famous theory of the experience of pain (Melzack & Wall, 1965; see Chapter 5) is just that: a theory about one and only one psychological experience, pain.

Scientific theories and scientific evidence are connected by a two-way street. Sometimes the direction of travel is from theory to evidence. The scientist formulates a theory, develops a specific hypothesis based on that theory, and then designs research to test that hypothesis. You learned this in Chapter 1: A theory about how stereotypes affect performance generated a specific hypothesis about when stereotype threat effects would occur. Research conducted at person, mind, and brain levels of analysis tested that hypothesis.

The results of research determine scientists’ level of confidence in their theories. If a theory generates hypotheses that repeatedly are confirmed, confidence in the theory grows. However, if a theory’s hypotheses are disconfirmed by evidence, the theory needs to be either modified or abandoned.

In this “direction of travel,” from theory to evidence, theory comes first and data are collected after a theoretical prediction is made. In practice, however, this sequence is less common than you might think. Science often proceeds in the opposite direction: Investigators (1) gather scientific data and then (2) try to devise a theory that explains important patterns in the collected data.

When traveling in this direction—from evidence to theory—psychologists are engaged in the process of discovery. By collecting and analyzing data carefully, they might discover interesting phenomena that need to be explained. Patterns in the data motivate and guide the subsequent development of theory. As one psychologist put it:

Become intimately familiar with … the data. Examine them from every angle. … If a datum suggests a new hypothesis, try to find additional evidence for it elsewhere in the data. If you see dim traces of interesting patterns, try to reorganize the data to bring them into bolder relief. … [Look for] something—anything—interesting. … How does one discover a new phenomenon? Smell a good idea? Have a brilliant insight into behavior? Create a new theory? [By] exploring the data.

—Bem (1987, p. 172)

You will see throughout this book that both directions of travel between theory and research have advanced the science of psychology.

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