If the two variables are related positively, we have observed that if the score on one variable is above the mean, then the score on the other variable will also tend to be above the mean. Earlier in Chapter 6, we learned about z-scores. A z-score tells us how far above (or below) the mean a score is in standardized units. Thus, in a positive relationship, the z-scores for the two variables should tend to agree; in particular, they both should be positive. In the scatterplot below, the two z-scores (in red, one for the horizontal variable and one for the vertical variable) are displayed for each point when you move your mouse near the point. Observe how the z-scores do or do not agree for a point for different values of the correlation coefficient. The green numbers count the number of points in each quadrant defined by the means.