The Neglect or Probability bias describes the tendency for our response to a threat to be proportionate to the type and form of threat and not the probability that it will occur. If something is extremely unlikely, but particularly nasty, we may respond by giving it a disproportionate amount of thought or an exaggerated physical response. This is the Bias that can make you panic about what is swimming under your feet in the ocean, when the chances of a shark attack are minuscule!

Medical Communication Example:

An example of the Neglect of Probability Bias in medical communication is when a person reads the possible causes for a symptom or symptom set and then obsesses about the worst possible cause, even if it is extremely unlikely and there are far more likely and benign causes. Disproportionately obsessing over cancer as the cause for night sweats even though environmental factors and stress are far more likely causes. Linked to Cyberchondria.

Example of Utility:


To try and neutralise a disproportionate response to a differential diagnosis you should provide statistics of disease prevalence. In the written form this is a weak defence but a graphical representation such as a pie chart helps humans quantify probability better (something we are notoriously bad at). Another solution is to include comparable statistics without an emotional investment such as “You are statistically more likely to win the lottery than have Disease X.”.

You should also try to include a plan to help people take control of a situation as taking control is a proven method for patients to reducing anxiety. “If you are worried that your symptoms may be related to HIV then click here for further help and advice, book an appointment at your local centre, etc.


If as a pharmaceutical company you are looking to uncover patients with a particular unusual disease you can use the Neglect of Probability Bias to motivate people to get checked or approach a GP with information on your disease type. Porphyria is a rare disease that can cause acute stomach pain, simply by appearing in the differential diagnosis webpages for ‘Stomach Pain’ this bias would nudge people to go and get screened despite the extremely unlikely nature.