A technique used to measure the likelihood of two behaviors relating to each other.
Psychologists are often interested in deciding whether two behaviors tend to occur together. One means of making this assessment involves using correlations. Sometimes two measurements are associated so that when the value of one increases, so does the other— a positive correlation. On the other hand, one value may increase systematically as the other decreases—a negative correlation.
For example, the number of correct answers on a student's test is generally positively related to the number of hours spent studying. Students who produce more correct answers have spent more hours studying; similarly, fewer correct answers occur with fewer hours spent studying.
One could also see whether the number of wrong answers on a test is associated with study time. This pattern is likely to produce a negative correlation: a greater number of wrong answers is associated with less study time. That is, the value of one variable increases (wrong answers) as the other decreases (hours spent studying).
Correlations allow an assessment of whether two variables are systematically related within a group of individuals. A single person may show behavior that differs from most of the rest of the group. For example, a given student might study for many hours and still not perform well on a test. This does not mean that study time and test grades are not related; it only means that exceptions exist for individuals, even if the rest of the group is predictable.
It is critical to remember that correlational approaches do not allow us to make statements about causation. Thus, greater study time may not necessarily cause higher grades. Students who are interested in a particular subject do better because of their interest; they also study more because they like the material. It may be their interest that is more important than the study time. One of the limitations of the correlational method is that although one variable (such as study time) may have a causal role on the other (such as test scores), one does not know that for certain because some other important factor (such as interest in the material) may be the most important element associated with both greater study time and higher test scores. When a third element is responsible for both variables (increase in study time and increase in grades), psychologists refer to this as the third variable problem.
The British scientist Sir Francis Galton developed the concept of the correlational method. The British statistician Karl Pearson (1857-1936) worked out the mathematical formulation. There are several different types of correlations; the most commonly used is called the Pearson Product-Moment Correlation.