Exponential Correlation

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Chapter 6


If you are dealing with a relationship between two variables that is exponential, there is a simple trick you can use to turn this very non-linear relationship into one you can test with the linear correlation coefficient. Since y = A x exp(Bt) is, taking the log of both sides, equivalent to log(y) = log(A) + B x t, you can cast the exponential relationship between y and t into a linear relationship between log(y) and t. Plotting the data using the log of y on one axis and the simple value of t on the other will display a straight line relationship if the intrinsic relationship is exponential. Computing r for the log(yi), ti pairs will tell you how significant the correlation is (i.e., how well an exponential describes the relationship between the two variables).

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