Differentiating qualitative and quantitative risk assessment techniques

The main difference between qualitative and quantitative risk assessment is that the former uses a relative or descriptive scale to measure the probability of occurrence whereas quantitative analysis uses a numerical scale.

For example, a qualitative analysis would use a scale of “Low, Medium, High” to indicate the likelihood of a risk event occurring.
A quantitative analysis will determine the probability of each risk event occurring. For example, Risk #1 has an 80% chance of occurring; Risk #2 has a 27% chance of occurring, and so on.