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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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