Watch for
Dismissing evidence with "that cannot be right" without examination.
Belief & ConfidenceBias #102
Semmelweis Reflex
We reject new evidence that contradicts established beliefs.
The reflex-like rejection of new scientific evidence or facts simply because they contradict established social norms paradigms or beliefs.
Why it matters: Named after Ignaz Semmelweis who discovered handwashing benefits but was rejected by peers.
Try this
When evidence contradicts belief evaluate the evidence quality before rejecting.
Real-world example
The medical establishment rejected Ignaz Semmelweis evidence that handwashing reduced mortality because it contradicted existing medical theory.
Key researchers
Ignaz Semmelweis
First described in 1850
Psychological mechanism
Paradigm protection and identity defense. Challenging established beliefs threatens social identity and professional standing. The brains first response is defensive rejection protecting the existing mental model.
Seminal research
Ignaz Semmelweis (1861) work on childbed fever and the rejection of his handwashing findings by the medical establishment.
Related Biases
Below is a realistic scenario. Read it, then choose what you would do. The feedback will show whether a cognitive bias influenced your choice — not to judge, but to reveal the pattern in action.
Thought Experiment
This experiment places you in a realistic decision. Your instinctive choice will reveal whether bias is at work.
STEP 1 → ReadSTEP 2 → ChooseSTEP 3 → Reveal
Debrief
The Semmelweis reflex shows that even scientists are not purely rational. Evidence that threatens established paradigms triggers an emotional rejection before cognitive evaluation. The remedy is to recognise the reflex and force yourself to evaluate disconfirming evidence on its merits.
Sources
Original ResearchSemmelweis (1861) — The etiology of childbed fever
EncyclopediaWikipedia overview