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relationship between X and Y (i.e., as X increases, Y decreases; see Fig. 6.5 ). In this
case, it is a negative correlation because the ‘‘football’’ you could draw around the data
points slopes down and to the right.
Fig. 6.5
Example of a scatterplot for a moderate, negative correlation (r =-0.39)
Figure 6.6 shows a perfect negative correlation of r =-1.0 which means that
X is a perfect predictor of Y, although in an inverse relationship such that as X
increases, Y decreases. The data points fit perfectly along a downward-sloping
straight line (see Fig. 6.6 ).
Fig. 6.6
Example of a scatterplot for a perfect, negative correlation (r =-1.0)
Let’s explain the formula for computing the correlation r so that you can
understand where the number summarizing the correlation came from.
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