3.3 Why lines are so ubiquitous and important as models

Simplicity - a critical modeling principle. A straight line models is about as simple as it gets:

$$\fbox{$y = b + m \times x.$ }$$

Transform to achieve linearity:

Cell phone subscribers

Transformed subscribers.

Transformed subscribers with line.

Approximation:

Empirical relationship;

Modeled relationship;

Zoom in,

Language: locally linear.