NR 511 COMMON COGNITIVE ERRORS IN
DIAGNOSTIC REASONING — LATEST STUDY
GUIDE 2026
1. Aggregate Bias
Definition: Believing population-based guidelines or evidence don’t apply to
your individual patient.
Example: A provider orders a chest X-ray for every cough because “my
patients are different,” even though guidelines say it’s unnecessary.
2. Anchoring
Definition: Fixating on initial information and ignoring new data that contradicts
it.
Example: Diagnosing a patient with “asthma exacerbation” on arrival and
overlooking later signs of heart failure.
3. Ascertainment Bias
Definition: Diagnostic thinking shaped by prior expectations, stereotypes,
or personal experience.
Example: Assuming a woman’s chest pain is anxiety-related rather than
cardiac.
4. Availability Bias
Definition: Judging a diagnosis as more likely because it’s easy to recall or
recently seen.
Example: After seeing several pneumonia cases, a provider overdiagnoses
pneumonia in a patient with viral bronchitis.
5. Base-Rate Neglect
Definition: Ignoring how common or rare a disease actually is.
Example: Ordering a CT for a rare brain tumor in a patient with a typical
tension headache.
, 6. Commission Bias
Definition: The urge to act rather than wait, even when action may not
help.
Example: Prescribing antibiotics “just in case” for a likely viral illness.
7. Confirmation Bias
Definition: Seeking data that supports your diagnosis while ignoring data
that refutes it.
Example: Not ordering a strep test after seeing “red throat” because you
already decided it’s viral.
8. Diagnosis Momentum
Definition: Once a label is attached, it sticks — regardless of accuracy.
Example: A chart says “COPD,” so every new provider assumes that
diagnosis without re-evaluation.
9. Feedback Sanction
Definition: Lack of feedback on past errors prevents learning.
Example: A misdiagnosis isn’t discovered until months later, so the provider
never knows or corrects the reasoning.
10. Framing Effect
Definition: Decisions influenced by how information is presented.
Example: Saying “90% survival rate” versus “10% mortality” changes
perception of risk.
11. Fundamental Attribution Error
Definition: Blaming patients for their illness instead of considering
situational causes.
Example: Assuming a homeless patient’s infection is due to “poor choices”
rather than lack of access to care.
DIAGNOSTIC REASONING — LATEST STUDY
GUIDE 2026
1. Aggregate Bias
Definition: Believing population-based guidelines or evidence don’t apply to
your individual patient.
Example: A provider orders a chest X-ray for every cough because “my
patients are different,” even though guidelines say it’s unnecessary.
2. Anchoring
Definition: Fixating on initial information and ignoring new data that contradicts
it.
Example: Diagnosing a patient with “asthma exacerbation” on arrival and
overlooking later signs of heart failure.
3. Ascertainment Bias
Definition: Diagnostic thinking shaped by prior expectations, stereotypes,
or personal experience.
Example: Assuming a woman’s chest pain is anxiety-related rather than
cardiac.
4. Availability Bias
Definition: Judging a diagnosis as more likely because it’s easy to recall or
recently seen.
Example: After seeing several pneumonia cases, a provider overdiagnoses
pneumonia in a patient with viral bronchitis.
5. Base-Rate Neglect
Definition: Ignoring how common or rare a disease actually is.
Example: Ordering a CT for a rare brain tumor in a patient with a typical
tension headache.
, 6. Commission Bias
Definition: The urge to act rather than wait, even when action may not
help.
Example: Prescribing antibiotics “just in case” for a likely viral illness.
7. Confirmation Bias
Definition: Seeking data that supports your diagnosis while ignoring data
that refutes it.
Example: Not ordering a strep test after seeing “red throat” because you
already decided it’s viral.
8. Diagnosis Momentum
Definition: Once a label is attached, it sticks — regardless of accuracy.
Example: A chart says “COPD,” so every new provider assumes that
diagnosis without re-evaluation.
9. Feedback Sanction
Definition: Lack of feedback on past errors prevents learning.
Example: A misdiagnosis isn’t discovered until months later, so the provider
never knows or corrects the reasoning.
10. Framing Effect
Definition: Decisions influenced by how information is presented.
Example: Saying “90% survival rate” versus “10% mortality” changes
perception of risk.
11. Fundamental Attribution Error
Definition: Blaming patients for their illness instead of considering
situational causes.
Example: Assuming a homeless patient’s infection is due to “poor choices”
rather than lack of access to care.
