Choice of the functional form

Exponential function
Exponential functions are functions which can be represented by graphs similar to the graph on the right

Yellow = 4x Green = ex
Black = 3x Red = 2x

As you could see in the graph, the larger the base, the faster the function increased
If we place a negative sign in front of the x, the graphs will be reflected(flipped) across the y-axis

Yellow = 4-x Green = e-x
Black = 3-x Red = 2-x

Exponential function
Exponential functions decrease if 0 < b1 < 1 and increase if b1 > 1

Power function

Logarithmic function

Hyperbolic function

Quadratic function

Logistic function

General information
NONLINEAR MODELS OFTEN ARE USED FOR SITUATION IN WHICH THE RATE OF INCREASE OR DECREASE IN THE DEPENDENT VARIABLE (WHEN PLOTTED AGAINST A PARTICULAR INDEPENDENT VARIABLE) IS NOT CONSTANT.

General information
SOME OF THESE MODELS REQUIRED A TRANSFORMATION TO THE INDEPENDENT VARIABLE.

Transformation
Logarithms
Substitution
Data transformations can be used to convert an equation into a linear form

Exponential function

Power function

Quadratic function

Polynomial function

Hyperbolic function

Logarithmic function

Logistic function

Linear function

Exponential function

Power function

Comparison

Comparison