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Negation
What is negation?
General description
- Negation describes the absence, or uncertainty about the presence of, a condition entity.
- The purpose of the negation signal is to capture negation and uncertainty
- The starting point for negation is that we need to mark conditions that a patient does not have. This is partly so that the computerised annotation can avoid reporting them as conditions of the patient. If we were to report all conditions that appear in a document, often we would be in the embarrasing position of reporting all patients with "no evidence of melanoma" as having melanoma.
- It is therefore important not only to annotate conditions, but also to mark those that are mentioned because the patient does not have them.
- Absence is always explicitly stated.
- For example
- "There was no evidence of lymphadenopathy"
- "no evidence" will be annotated as a negation signal with value absent.
- Negation will only ever be annotated when it relates to a condition.
- Note that we are not concerned that "absence of evidence is no evidence of absence". We are interested in capturing negative signals in the text, and will assume, for the purposes of annotation, that "no evidence" and other such signals are the same as absence.
For every negation, annotate a modifier relation
For every negation signal, at least one modifier relation must also be annotated, relating it to the associated condition.
For every negation, select a value
Each Negation signal that is annotated will be assigned a value from the enumeration: {absent, uncertain}.
- For example:
- "There was no evidence of skin metastases"
- The signal "no evidence" signals that "metastases" do not exist.
- "no evidence" will be annotated as a negation entity with value of absent.
- For example:
- "? METASTASIS"
- The signal "?" signals that the existence of "metastases" is uncertain.
- "?" will be annotated as a negation entity with value of uncertain.
- For example:
- "The diagnosis of myelodysplasia is uncertain"
- The signal "uncertain" signals that "myelodysplasia" might not exist.
- "uncertain" will be annotated as a negation entity with value of uncertain.
Annotate the entire phrase
- Absence may be signalled by a single word, such as "no", but is often signalled by an entire phrase. The entire phrase that signals the absence should be marked.
- For example,
- "failed to indicate a definitive diagnosis of malignancy"
- The "malignancy" is being negated by a phrase, "failed to indicate".
- The entire phrase should be annotated.
- For example,
- "no evidence on this swallow of progressive disease."
- the disease is being negated by the entire phrase "no evidence", which should be annotated.
Examples of stock phrases
Other stock phrases that indicate negation entities include:
- "free from"
- "absent"
- "no"
- "not present"
- "not seen"
- "uncertain"
- "unsure"
- "no evidence"
- "?" (as in query) - a negation with value of uncertain.
What is not negation?
Entities other than conditions are not negated
Only conditions will be negated. If a phrase describes the existence of something other than a condition, then it will not be annotated.
-
- For example,
- "no evidence of surgery"
- "no evidence" will not be annotated as a negation entity
Conditions that are already expressed in the negative
Negation is not about marking conditions that are already negatives
- For example,
- "afebrile"
- "Afebrile" should not be marked as a negation. It is already a negative.