Probability and Evidence


This collection of resources was developed in collaboration with Professor Philip Dawid of the University of Cambridge



The problems in this collection are about thinking about which questions to ask, and how to interpret the answers.

For example, almost everyone who gets measles gets spots. If you go to your doctor with spots, they won't conclude that you're very likely to have measles, as there are many other diseases that can cause spots.

You need to be careful about the difference between the probability of getting spots if you have measles and the probability of having measles if you get spots. This mistake has caused numerous misunderstandings in medicine, law and wider society.

Introductory Video

Age 11 to 16

An introductory video to the Probability and Evidence collection

Spots and Measles

Age 11 to 16 Challenge Level:

99% of people who have measles have spots. Ben has spots. Do you think he has measles?

Evidence and Headlines

Age 11 to 18

Headlines sometimes distort the truth. Read about how micromorts can be used to compare the risks of different activities.

Probability in Court

Age 14 to 18 Challenge Level:

When you're on trial for murder, it can be crucial that the court understands probability...

Do Rare Events Happen?

Age 11 to 16 Challenge Level:

I'd be very surprised if I had three children all with the same birthday, but I read in the paper that it happened to one family...

Matching Criminals

Age 14 to 18 Challenge Level:

DNA profiling is an invaluable tool for the police. However, when it comes to probability, things aren't always as straightforward as they seem.

The ELISA Test

Age 14 to 18 Challenge Level:

In 1% of cases, an HIV test gives a positive result for someone who is HIV negative. How likely is it that someone who tests positive has HIV?


These resources were originally developed by the Millennium Mathematics Project Motivate Programme in collaboration with Professor Philip Dawid, funded by a Wellcome Trust grant.