One form of error is over-generalizing. This occurs when we arrive at some conclusion or make a generalization based on limited information. Let's say you meet some fellow students from a certain area of your country and all said they came from large families. On this basis, you might be tempted to tell others that all families in that area have large numbers of children. If you did, you would be over-generalizing because you don't have data about all or even a large number of the families in that area. Some families might include only a few or even no children. Researchers limit their conclusions to what their data clearly support.

Another kind of common error is to reach a conclusion before all the data are examined. This is called premature closure. Let's go back to the example of family sizes. Suppose you decided to investigate the actual sizes of the families living in a certain area. Let's say you asked the heads of 20 families out of several hundred living in the area how many persons reside in their households. You find that most have large numbers of members, but some do not. If you stopped collecting data at that point and concluded that, indeed, most families are large you would probably be making the error of premature closure. In effect, you closed your mind to new information. To safely generalize about sizes of families in the area, you would need to collect data from a much larger number of families representing the entire group of families.

We are also prone to selective observation, another common error in forming conclusions based on experience. As the name implies, we select certain experiences and ignore others. Often, the experiences we select are ones that agree with our values or prejudices. We look for what we expect to find. Using the family size example yet again, suppose you had been told repeatedly that people living in the area in question all want to have many children. You meet a few students from the area and find they also want to have large families, which reinforces what you expected to hear. In addition, suppose you also meet an equal number of students from the area who say they want only a few children. Without being consciously aware of it, you might disregard the reports that are contrary to your expectation and form your conclusion based on only on the reports that agreed with what your expected to hear.

As researchers, we have to guard against generalizing beyond the data we have; closing our minds to additional data; or selecting only certain findings and ignoring other data when we are forming generalizations. In later chapters, you will learn how to avoid these kinds of errors.

Origins of the scientific approach

Beginning in about the 16th century in Europe, a small number of men began to question traditionally accepted beliefs about the natural world. One of these early scientists was Galileo Galile, an Italian. As students, men like Galileo and others before him, learned what educated persons had been taught for over a thousand years. Beliefs about the natural world were then based on what Aristotle, a Greek philosopher, had written about 1,000 years earlier. One of these "truths" was that the earth was the center of the universe; another was that the sun revolved around the earth.

But the early scientists began to question these beliefs. Based on their observations of the movements of the sun, planets, and other bodies in the universe, they saw a different pattern. Their observations convinced them that the earth was not the center of the universe and that the earth circled the sun and not the other way around. Instead of accepting the traditional beliefs of their age, they reported their observations and conclusions. Other scientists, at great risk from religious authorities who defended the traditional beliefs, repeated the studies of earlier scientists and came to similar conclusions.

Based on the agreement among their observations, these early scientists gained confidence in their methods and, after a struggle lasting several centuries, succeeded in establishing a new way of inquiring about the natural world. In several centuries, the scientific method of inquiry spread from the study of the physical things, to biology and later to the study of the human mind and human behavior and, lastly, to the investigation of social life. Today, the scientific approach is accepted worldwide as the best way of establishing knowledge about what we can observe. This includes understanding how social relationships develop and are carried out.

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