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From "Miller, Timothy" <Timothy.Mil...@childrens.harvard.edu>
Subject Re: cTakes polarity problem
Date Wed, 31 Dec 2014 15:13:37 GMT
Hi Yu,

The new polarity module is machine-learning based so it is not always
easy to diagnose accuracy issues. But generally it might mean there was
no example like that in the training data. It was trained on multiple
corpora, but sometimes certain phrases slip through the cracks, and
"Deny hepatitis," while possible in the truncated language of clinical
notes, seems like an unlikely phrase and so it may not be in our data.
Is that a real example you saw or just a minimum (not) working example?
If not do you have a real example (i.e. a whole sentence) where "deny"
should cause a negation but does not? If so I will look into it. We have
had a few reports like this so it may be worth keeping track of missed
examples for future iterations of the module. It is important that they
be real examples "from the wild" though.

(As an aside, machine learning methods don't understand language the way
people do so even if it seems obvious to a human that "Deny <disease>."
should be negated, if it looks different enough from the context of an
example from the training data the ML will sometimes fall back to the
majority class of "Not negated".)

Tim


On 12/31/2014 10:03 AM, Yu Liang wrote:
> I have a quick question about CTAKES.
> I am using AE “AggregatePlaintextUMLSProcessor.xml” and want to get some negation
results by referring to polarity attribute.
> However, it turns out, for example “Negative for hepatitis”, is not negated. I think
it is weird and I tried “No hepatitis”, “ Denies hepatitis” which return “polarity=
-1”, but “Deny hepatitis.” returns “polarity=1”.
>
> any one could give me some clue that what is wrong? Thank you!


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