Watch for
Updating beliefs based on new evidence without considering base rates.
Outcome & SelfBias #137
Neglect of Prior Probability
We ignore prior probabilities when updating beliefs.
The tendency to update beliefs or probabilities without factoring in the original baseline probability of an occurrence.
Why it matters: Related to the base rate fallacy. A core concept in Bayesian reasoning.
Try this
Always start with the prior probability before incorporating new evidence using Bayes rule.
Real-world example
Hearing a witness identify a blue car in a hit-and-run and concluding it is likely blue without considering that most cars in the area are silver.
Key researchers
Daniel Kahneman, Amos Tversky
First described in 1973
Psychological mechanism
Representativeness heuristic override. New evidence that is vivid and story-like dominates judgment while abstract prior probabilities are underweighted or ignored.
Seminal research
Amos Tversky and Daniel Kahneman (1973), "On the psychology of prediction."
Related Biases
Debrief
Biases are not character flaws. They are recurring patterns in how minds compress uncertainty, save energy, and narrate reality. Once you recognise the pattern, you can slow the decision down, test the assumption, and make space for a better explanation.
Sources
Original ResearchTversky and Kahneman (1973) — Prior probability neglect
EducationalAPA Dictionary entry