if the correlation between x and y is equal to -1.0, then we know that the prediction of y by x is perfect
The correlation coefficient is a unitless number and must always lie between –1.0 and +1.0, inclusive.
The correlation coefficient, r , gives us information about the strength and direction of a linear relationship between any two variables. (r > 0 is a positive correlation, r < 0 is negative, and |r| closer to 1 means a stronger correlation.
The larger r is in absolute value, the stronger the relationship is between the two variables.
If r is the correlation between two variables x and y then -r is the correlation between y and x
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