This correlation meter is designed to help you understand the relationship between a correlation coefficient (shown in red in the upper right of the meter) and a scatter diagram of scores for variable one and two. Imagine, for example, that each dot represents the scores that a student received on a quiz (Variable 1) and on a midterm test (Variable 2).
Click on and hold the mouse down on the slider at the bottom of the meter. Move it to the left and right. As you do so you will see that as the correlation coefficient changes the dots also change.
What is the Correlation?
Recall that correlation is a measure of direction and degree of relationship between two variables. A correlation coefficient is a numerical index of that relationship. A positive (measure of direction) correlation or direct relationship is indicated by a positive (+) sign before the coefficient. This indicates that a high score on one variable is associated with a high score on the second variable. A negative correlation or inverse relationship is indicated by a negative (-) sign before the coefficient. This indicates that a high score on one variable is associated with a low score on the second variable.
The magnitude of the correlation coefficient indicates the strength of the relationship between the two variables. This magnitude can vary from 0.00 to 1.00. Move the slider all the way to the right. This shows a perfect positive correlation (+1.00). Move the slider all the way to the left. This shows a perfect negative (-1.00) correlation. The closer the correlation coefficient is to either -1.00 or +1.00 the stronger the relationship.
One more thing about the usefulness of correlation. If two variables are known to be strongly related, we can predict one from the other. The more strongly two variables are related, the better the prediction. Social and natural scientists use correlation all the time to help them make predictions. For instance, psychologists know that there is a fairly strong relationship (about +.50 to +.60) between scores on the SAT or ACT test and grades in college. Therefore, some colleges use these test scores as admittance requirements (meaning a high test score is associated with high grades, success, in college).