Base rate fallacy
Also called: Ignoring the starting odds
Judging a probability from a striking detail while ignoring how common the thing is overall.
How to spot it
How common is this outcome before you add the new information?
Example
“The test is 95% accurate and I tested positive, so I almost certainly have it.” (If the condition is very rare, most positives are false.)
How to answer it
Start from how common it is, then adjust.
Related
- Conjunction fallacy: Thinking two things together are more likely than one of them alone.
- Gambler's fallacy: Believing that past random results change the odds of the next one.