Negation Detection in Swedish Clinical Text Maria Skeppstedt PhD Student at Stockholm University Department of Computer and Systems Sciences.

Negation Detection in Swedish Clinical Text

Maria Skeppstedt

PhD Student atStockholm University

Department of Computer and Systems Sciences

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Why do you need negation detection in clinical text?

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Record X

Since the patient has

no headache, the

patient does probably

not have disease A.

Record Y

The patient has a

headache.

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A first step towards Swedish negation detection

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NegEx

By Wendy W Chapman, Will Bridewell, Paul Hanbury, Gregory F. Cooper, and Bruce G. Buchanan

Basic idea of NegEx

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Since the patient has no headache, … (headache)

The patient has not only a headache, but also … (headache)

Pre-Triggers

no

not

no signs of

…

Post-Triggers

unlikely

…

Pseudo negation

not only

…

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Translation of negation triggers

• no ->ingen

• not -> inte

• no signs of -> inga tecken

• …

• not only -> inte bara

• …

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Grammatical differences, Swedish and English, examples

1. Gender and number concord: ”no’’ -> ”inga” (plural), ”ingen” (common gender) and ”inget” (neuter gender)“no significant” -> ”inga signifikanta” (plural), “ingen signifkant” (common gender) and “inget signifikant” (neuter gender)

2. ”denies/is denying” -> no grammatical equivalent in Swedish

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Construction of test data

1. Diseases and symptoms from the describing text of the ICD-10 codes

2. Automatic pre-processing of ICD-10 codesFor example: “migraine, not specified” -> “migraine”

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Classification of test data

1. 430 sentences

2. Affirmed, negated and ambiguous

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Results, group 1, sentences with trigger phrases

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Results, group 2, sentences without trigger phrases

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Triggers for correctly identified negations

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Precision for different triggers

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Examples of errors, that account for some of the difference

1. ”inga egentliga märkbara symptom …” (no real noticeable symptoms …)

2. ”Hon har inte huvudvärk, utan tandvärk ” (She has not headache, but toothache)

3. ”icke allergisk astma” (non-allergic asthma)

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Examples of other errors

1. ”Patienten har inte huvudvärk, men bröstsmär- tor.” (The patient has no headache, but chest pain)

2. ”Om inte huvudvärken har vikit ...” (If not the headache has disappeared)

3. ”Cirka hälften av alla med sjukdom A har inte symptom B” (About half of those with disease A, have no symptoms of B)

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The next step

1. A list of conjunctions that limit the scope of the trigger.

2. Elaborate with adding or removing trigger phrases from the list.

3. Evaluation on a larger test set.

4. Detect the meaning of “utan” (but/without) in the context, and which cases that the trigger “not” negates.

Thank you!

Questions?

Maria Skeppstedt

[email protected]