Chapter 2 Uncertainty

In 2008, Kennedy Brewer was exonerated after 15 years in prison for the brutal murder of his then-girlfriend’s 3 year old child. Expert testimony had claimed that marks found on the body of the child had been bite marks and had without a doubt been caused by Brewer. The expert’s belief did not accurately reflect the uncertainty in the scientific understanding of bite mark evidence.

Becoming familiar with uncertainty is the basis for thinking about probability and statistics, and ultimately evaluating scientific evidence. In this chapter, we will define what is meant by uncertainty, how different types of uncertainty can be characterised, give an example of uncertainty in scientific evidence, and finally discuss the communication of uncertainty.