Chapter 10. Intelligence

Statistical Lesson. As the text explains, when we measure a correlation we will typically get a correlation coefficient, a mathematical measure of both the direction and strength of a correlation. It is most commonly represented by the letter r. This value for the correlation tells us how strong the correlation is and the direction of the correlation. The strength of a correlation can range from 0 to ±1. The closer r gets to 1, the stronger the relationship is between the variables, while the closer r gets to 0, the weaker the relationship.

The following table provides a guide to the various strengths based on the value (so only look at the number and not the sign before it):

The sign for the correlation tells us whether the correlation is positive (greater than 0) or negative (less than 0).

• An r with a positive (+) sign or no sign is considered positive. A positive correlation means that as one variable increases, so does the other, which is evident in an upward sloping line or data in a graph.

• An r with a negative (-) sign is considered negative. A negative correlation means that as one variable increases, the other decreases, which is evident in a downward sloping line or data in a graph.

Remember the coverage on correlation in the applet for Emotion & Motivation? We discussed the importance of remembering that when considering relationships between variables, we cannot conclude that one of the variables caused the change we see in the other variable. This is especially true when we do not conduct an experiment that included manipulation or control over the variables or environment being studied. Studies of intelligence are great examples of naturalistic studies where we cannot manipulate, but only measure our variables. However, the way these studies are design can lead us to further pinpoint what might contribute to the relationship or differences we see. For example, comparing siblings or twins raised apart with those who are reared together can give us insight into how much a shared environment or genetics contribute to IQ. As always, keep in mind when interpreting relationship to not infer causality, and always look for confounding variables.