# Probability

From ACT Wiki

The study of chance providing an objective measure of uncertainty.

Probabilities range between 1 (= 100%) and 0 (= 0%).

A probability of 100% means that an event is considered certain to occur.

A probability of 0% means that an event is considered certain not to occur.

For example, flipping an unbiased coin, the probability of getting a head is often modelled as 50%.

### The problem

This simple model of a coin flip assumes that the only two possibilities are a head or a tail.

Applying such simple models to financial situations, and treating financial outcomes as simple coin flips, may lead to errors resulting from:

- The coin landing on its edge 'more often than it's supposed to'.
- The underlying assumption of an unbiased coin not being a valid one. This kind of assumption is usually much too simple.