Descriptive models vs Predictive Models

Analogy → Categories design spaces → Analytic Statistics → Equations

Fitts law

Fitts’ Law is a fundamental model in Human–Computer Interaction (HCI) that predicts how long it takes a user to move to and select a target (like clicking a button).

The time to click something depends on two things:

1. Distance to the target
2. Size of the target

Fitts’ Law is commonly written as:

$$ MT = a + b \cdot \log_2\left(\frac{D}{W} + 1\right) $$

Where:

• MT = Movement Time (how long it takes to click)
• D = Distance to the target
• W = Width of the target
• a, b = constants determined experimentally

The difficulty of clicking something increases when:

• the distance increases
• the target becomes smaller