Base rate neglect is best described as:

• A. Ignoring base rates when evaluating the probability of an event after new evidence
• B. Overestimating how often a rare event occurs due to vivid examples
• C. Believing that a pattern is due to a single cause
• D. Remembering the first and last items in a sequence

Answer: (A)

Base rate neglect is the tendency to ignore base rates when evaluating the probability of an event after new evidence. People focus on the new information or vivid details and forget the prior likelihood of the event in the population, which can distort probability judgments.

For example, if a disease affects only 1% of people, even a test with 95% accuracy can yield many false positives relative to true positives. A person who tests positive might think they almost certainly have the disease, but the actual probability is around 16% when you account for the base rate. This illustrates how ignoring base rates leads to misjudging likelihoods.

The other options describe different biases: overestimating a rare event due to vivid examples is about how memorable instances skew perception; attributing a pattern to a single cause is a different explanatory bias; and recalling only the first and last items reflects a memory effect. The described tendency aligns with base rate neglect.