How to evaluate NLP tools for entity extraction

1. How to Evaluate NLP Tools for Entity Extraction
Gil Irizarry
VP Engineering
[Apple | Organization] and [Oranges | Fruit]:

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About Rosette
Trusted In Critical Applications By

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About Me
Gil Irizarry - VP Engineering at Basis Technology, responsible for NLP and Text
Analytics software development
https://www.linkedin.com/in/gilirizarry/
https://www.slideshare.net/conoagil
gil@basistech.com
Basis Technology - leading provider of software solutions for extracting
meaningful intelligence from multilingual text and digital devices

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Agenda
● The problem space
● Defining the domain
● Assemble a test set
● Annotation guidelines
● Review of measurement
● Evaluation examples
● Inter-annotator agreement
● The steps to evaluation

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Rosette Capabilities

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The Problem Space
● You have some text to analyze. Which tool to choose?
● Related question: You have multiple text or data annotators. Which are doing
a good job?
● The questions are made harder by the tools outputting different formats,
analyzing data differently, and annotators interpreting data differently
● Start by defining the problem space

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The Problem Space - Example
Rosette Amazon Comprehend

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Defining the domain
● What space are you in?
● More importantly, in what domain will you evaluate tools?
● Are you:
○ Reading news
○ Scanning patents
○ Looking for financial fraud

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Assemble a test set
● NLP systems are often trained on a general corpus. Often this corpus
consists of mainstream news articles.
● Do you use this domain or a more specific one?
● If more specific, do you train a custom model?

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Annotation Guidelines
Examples requiring definition and agreement in guidelines:
● “Alice shook Brenda’s hand when she entered the meeting.” Is “Brenda” or
“Brenda’s” the entity to be extracted (in addition to Alice of course)?
● Are pronouns expected to be extracted and resolved? “She” in the previous example
● What about tolerance to punctuation? The U.N. vs. the UN
● Should fictitious characters (“Harry Potter”) be tagged as “person”?
● When a location appears within an organization’s name, do you tag the location and the
organization extracted or just the organization (“San Francisco Association of
Realtors”)?

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Annotation Guidelines
Examples requiring definition and agreement in guidelines:
● Do you tag the name of a person if it is used as a modifier (“Martin Luther King Jr.
Day”)?
● Do you tag “Twitter” in “You could try reaching out to the Twitterverse”?
● Do you tag “Google” in “I googled it, but I couldn’t find any relevant results”?
● When do you include “the” in an entity? The Ukraine vs. Ukraine
● How do you differentiate between an entity that’s a company name and a product by
the same name? {[ORG]The New York Times} was criticized for an article about the
{[LOC]Netherlands} in the June 4 edition of {[PRO]The New York Times}.
● “Washington and Moscow continued their negotiations.” Are Washington and
Moscow locations or organizations?

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Annotation Guidelines
Non-entity extraction issues:
● How many levels of sentiment do you expect?
● Ontology and text classification - what categories do you expect?
● For language identification, are dialects identified as separate languages?
What about macrolanguages?

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Annotation Guidelines

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Annotation Guidelines
● Map to Universal Dependencies Guidelines where possible:
https://universaldependencies.org/guidelines.html
● Map to DBpedia ontology where possible:
http://mappings.dbpedia.org/server/ontology/classes/
● Map to known database such as Wikidata where possible:
https://www.wikidata.org/wiki/Wikidata:Main_Page

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Review of measurement: precision
Precision is the fraction of retrieved documents that are relevant to the query

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Review of measurement: recall
Recall is the fraction of the relevant documents that are successfully retrieved

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Review of measurement: F-score
F-score is a harmonic mean of precision and recall
Precision and recall are ratios. In this case, a harmonic mean is more appropriate
for an average than an arithmetic mean.

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Review of measurement: harmonic mean
A harmonic mean returns a single value to combine both precision and recall. In
the below image, a and b map to precision and recall, and H maps to F score. In
this example, note that increasing a would not increase the overall score.

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Review of measurement: F-score
Previous example of F score was actually an F1 score, which balances precision
and recall evenly. A more generalized form of F score is:
F2 (β = 2) weights recall higher than precision and F0.5 (β = 0.5) weights precision
higher than recall

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Review of measurement: AP and MAP
● Average precision is a measure that combines recall and precision for ranked
retrieval results. For one information need, the average precision is the mean
of the precision scores after each relevant document is retrieved
● Mean average precision is average precision over a range of queries

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Review of measurement: MUC score
● Message Understanding Conference (MUC) scoring allows for taking partial
success into account
○ Correct: response = key
○ Partial: response ~= key
○ Incorrect: response != key
○ Spurious: key is blank and response is not
○ Missing: response is blank and key is not
○ Noncommittal: key and response are both blank
○ Recall = (correct + (partial x 0.5 )) / possible
○ Precision = (correct+(partial x 0.5)) / actual
○ Undergeneration = missing / possible
○ Overgeneration = spurious / actual

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Evaluation Examples
As co-sponsor, Tim Cook was seated at a
table with Vogue editor Anna Wintour, but
he made time to get around and see his
other friends, including Uber CEO Travis
Kalanick. Cook's date for the night was
Laurene Powell Jobs, the widow of Apple
cofounder Steve Jobs. Powell currently
runs Emerson Collective, a company that
seeks to make investments in education.
Kalanick brought a date as well, Gabi
Holzwarth, a well-known violinist.

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Evaluation Examples - gold standard
As co-sponsor, Tim Cook was seated at a
table with Vogue editor Anna Wintour, but
he made time to get around and see his
other friends, including Uber CEO Travis
Kalanick. Cook's date for the night was
Laurene Powell Jobs, the widow of Apple
cofounder Steve Jobs. Powell currently
runs Emerson Collective, a company that
seeks to make investments in education.
Kalanick brought a date as well, Gabi
Holzwarth, a well-known violinist.

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Evaluation Examples - P, R, F
● (Green) TP = 6
● (Olive) FP = 1
● (Orange) TN = 3
● (Red) FN = 3
● Precision = 6/7 = .86
● Recall = 6/9 = .66
● F score = .74

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Evaluation Examples - AP
● 1/1 (Green)
● 2/2 (Green)
● 3/3 (Green)
● 0/4 (Red)
● 4/5 (Green)
● 5/6 (Green)
● 0/7 (Red)
● 0/8 (Red)
● 6/9 (Green)
● AP = (1/1 + 2/2 + 3/3 + 4/5 + 5/6 +
6/9) / 6 = .88

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Evaluation Examples - MUC scoring
Token Gold Eval Result
Cook's B-PER B-PER Partial
Date O-NONE I-PER Spurious
For O-NONE O-NONE Correct
The O-NONE O-NONE Correct
Night O-NONE O-NONE Correct
Was O-NONE O-NONE Correct
Laurene B-PER B-PER Correct
Powell I-PER I-PER Correct
Jobs, I-PER O-NONE Missing
The O-NONE O-NONE Correct
widow O-NONE O-NONE Correct
Of O-NONE O-NONE Correct
Apple O-NONE B-ORG Spurious
cofounder O-NONE O-NONE Correct
Steve B-PER B-PER Correct
Jobs. I-PER I-LOC Incorrect

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Evaluation Examples - MUC scoring
Possible = Correct + Incorrect + Partial +
Missing = 11 + 1 + 1 + 1 = 14
Actual = Correct + Incorrect + Partial +
Spurious = 11 + 1 + 1 + 2 = 15
Precision = correct + (1/2 partial)) / actual =
12.5 / 15 = 0.83
Recall = (correct + (1/2 partial)) / possible =
12.5 / 14 = 0.89
Token Gold Eval Result
Cook's B-PER B-PER Partial
Date O-NONE I-PER Spurious
For O-NONE O-NONE Correct
The O-NONE O-NONE Correct
Night O-NONE O-NONE Correct
Was O-NONE O-NONE Correct
Laurene B-PER B-PER Correct
Powell I-PER I-PER Correct
Jobs, I-PER O-NONE Missing
The O-NONE O-NONE Correct
widow O-NONE O-NONE Correct
Of O-NONE O-NONE Correct
Apple O-NONE B-ORG Spurious
cofounder O-NONE O-NONE Correct
Steve B-PER B-PER Correct
Jobs. I-PER I-LOC Incorrect

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Inter-annotator Agreement
● Krippendorff ’s alpha is a reliability coefficient developed to measure the
agreement among observers,coders, judges, raters, or measuring
instruments drawing distinctions among typically unstructured phenomena
● Cohen’s kappa is a measure of the agreement between two raters who
determine which category a finite number of subjects belong to whereby
agreement due to chance is factored out
● Inter-annotator agreement scoring determines the agreement between
different annotators annotating the same unstructured text
● It is not intended to measure the output of a tool against a gold standard

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The Steps to Evaluation
● Define your requirements
● Assemble a valid test dataset
● Annotate the gold standard test dataset
● Get output from tools
● Evaluate the results
● Make your decision

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Thank You!
Gil Irizarry
VP Engineering
gil@basistech.com
https://www.linkedin.com/in/gilirizarry/
https://www.slideshare.net/conoagil