A correlation is the measurement of the relationship between two variables. These variables already occur in the group or population and are not controlled by the experimenter.
- A positive correlation is a direct relationship where as the amount of one variable increases, the amount of a second variable also increases.
- In a negative correlation, as the amount of one variable goes up, the levels of another variable go down.
- In both types of correlation, there is no evidence or proof that changes in one variable cause changes in the other variable. A correlation simply indicates that there is a relationship between the two variables.
The most important concept to take from this is that correlation does not equal causation. Many popular media sources make the mistake of assuming that simply because two variables are related, a causal relationship exists.
Further Reading:The Simple Experiment
Steps in Psychology Research