1.3.3.19.6. Scatter Plot: Exponential Relationship

Note that a simple straight line is grossly inadequate in describing the relationship between X and Y. As seen in the previous example, the simplest non-linear function is quadratic. We could fit a quadratic here but it would prove lacking--especially for large values of X. In this example, it appears that large values of X are yielding flat (= constant) values of Y. For the quadratic family, large values of X mathematically must yield large (positive or negative) values of Y-- hence a non-linear function beyond quadratic is needed. Among the many other non-linear functions available, one of the simpler is the exponential (Y = A + B*exp(C*X) for some A, B, and C). In this case, and exponential function would in fact fit well, and hence one is led to the summary conclusion: "exponential relationship".