Sentiment Analysis

What is Sentiment Analysis?

Dan Jurafsky

Positive or negative movie review?

• unbelievably disappointing
• Full of zany characters and richly applied satire, and some great plot twists
• this is the greatest screwball comedy ever filmed
• It was pathetic. The worst part about it was the boxing scenes.

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Dan Jurafsky

Google Product Search

• a

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Bing Shopping

• a

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Dan Jurafsky

Twitter sentiment versus Gallup Poll of Consumer Confidence

Brendan O'Connor, Ramnath Balasubramanyan, Bryan R. Routledge, and Noah A. Smith. 2010. From Tweets to Polls: Linking Text Sentiment to Public Opinion Time Series. In ICWSM-2010

Dan Jurafsky

Twitter sentiment:

Johan Bollen, Huina Mao, Xiaojun Zeng. 2011. Twitter mood predicts the stock market,

Journal of Computational Science 2:1, 1-8. 10.1016/j.jocs.2010.12.007.

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Dan Jurafsky

• CALM predicts DJIA 3 days later
• At least one current hedge fund uses this algorithm

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Dow Jones

CALM

Bollen et al. (2011)

Dan Jurafsky

Target Sentiment on Twitter

• Twitter Sentiment App
• Alec Go, Richa Bhayani, Lei Huang. 2009. Twitter Sentiment Classification using Distant Supervision

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Dan Jurafsky

Sentiment analysis has many other names

• Opinion extraction
• Opinion mining
• Sentiment mining
• Subjectivity analysis

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Dan Jurafsky

Why sentiment analysis?

• Movie: is this review positive or negative?
• Products: what do people think about the new iPhone?
• Public sentiment: how is consumer confidence? Is despair increasing?
• Politics: what do people think about this candidate or issue?
• Prediction: predict election outcomes or market trends from sentiment

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Dan Jurafsky

Scherer Typology of Affective States

• Emotion: brief organically synchronized … evaluation of a major event
• angry, sad, joyful, fearful, ashamed, proud, elated
• Mood: diffuse non-caused low-intensity long-duration change in subjective feeling
• cheerful, gloomy, irritable, listless, depressed, buoyant
• Interpersonal stances: affective stance toward another person in a specific interaction
• friendly, flirtatious, distant, cold, warm, supportive, contemptuous
• Attitudes: enduring, affectively colored beliefs, dispositions towards objects or persons
• liking, loving, hating, valuing, desiring
• Personality traits: stable personality dispositions and typical behavior tendencies
• nervous, anxious, reckless, morose, hostile, jealous

Dan Jurafsky

Scherer Typology of Affective States

• Emotion: brief organically synchronized … evaluation of a major event
• angry, sad, joyful, fearful, ashamed, proud, elated
• Mood: diffuse non-caused low-intensity long-duration change in subjective feeling
• cheerful, gloomy, irritable, listless, depressed, buoyant
• Interpersonal stances: affective stance toward another person in a specific interaction
• friendly, flirtatious, distant, cold, warm, supportive, contemptuous
• Attitudes: enduring, affectively colored beliefs, dispositions towards objects or persons
• liking, loving, hating, valuing, desiring
• Personality traits: stable personality dispositions and typical behavior tendencies
• nervous, anxious, reckless, morose, hostile, jealous

Dan Jurafsky

Sentiment Analysis

• Sentiment analysis is the detection of attitudes

“enduring, affectively colored beliefs, dispositions towards objects or persons”

• Holder (source) of attitude
• Target (aspect) of attitude
• Type of attitude
• From a set of types
• Like, love, hate, value, desire, etc.
• Or (more commonly) simple weighted polarity:
• positive, negative, neutral, together with strength
• Text containing the attitude
• Sentence or entire document

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Dan Jurafsky

Sentiment Analysis

• Simplest task:
• Is the attitude of this text positive or negative?
• More complex:
• Rank the attitude of this text from 1 to 5
• Advanced:
• Detect the target, source, or complex attitude types

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Dan Jurafsky

Sentiment Analysis

• Simplest task:
• Is the attitude of this text positive or negative?
• More complex:
• Rank the attitude of this text from 1 to 5
• Advanced:
• Detect the target, source, or complex attitude types

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Dan Jurafsky

Sentiment Analysis

What is Sentiment Analysis?

Dan Jurafsky

Sentiment Analysis

A Baseline Algorithm

Dan Jurafsky

Sentiment Classification in Movie Reviews

• Polarity detection:
• Is an IMDB movie review positive or negative?
• Data: Polarity Data 2.0:
• http://www.cs.cornell.edu/people/pabo/movie-review-data

Bo Pang, Lillian Lee, and Shivakumar Vaithyanathan. 2002. Thumbs up? Sentiment Classification using Machine Learning Techniques. EMNLP-2002, 79—86.

Bo Pang and Lillian Lee. 2004. A Sentimental Education: Sentiment Analysis Using Subjectivity Summarization Based on Minimum Cuts. ACL, 271-278

Dan Jurafsky

IMDB data in the Pang and Lee database

when _star wars_ came out some twenty years ago , the image of traveling throughout the stars has become a commonplace image . […]

when han solo goes light speed , the stars change to bright lines , going towards the viewer in lines that converge at an invisible point .

cool .

_october sky_ offers a much simpler image–that of a single white dot , traveling horizontally across the night sky . [. . . ]

“ snake eyes ” is the most aggravating kind of movie : the kind that shows so much potential then becomes unbelievably disappointing .

it’s not just because this is a brian depalma film , and since he’s a great director and one who’s films are always greeted with at least some fanfare .

and it’s not even because this was a film starring nicolas cage and since he gives a brauvara performance , this film is hardly worth his talents .

✓

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Dan Jurafsky

Baseline Algorithm (adapted from Pang and Lee)

• Tokenization
• Feature Extraction
• Classification using different classifiers
• Naïve Bayes
• MaxEnt
• SVM

Dan Jurafsky

Sentiment Tokenization Issues

• Deal with HTML and XML markup
• Twitter mark-up (names, hash tags)
• Capitalization (preserve for

words in all caps)

• Phone numbers, dates
• Emoticons
• Useful code:
• Christopher Potts sentiment tokenizer
• Brendan O’Connor twitter tokenizer

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[<>]? # optional hat/brow

[:;=8] # eyes

[\-o\*\']? # optional nose

[\)\]\(\[dDpP/\:\}\{@\|\\] # mouth

| #### reverse orientation

[\)\]\(\[dDpP/\:\}\{@\|\\] # mouth

[\-o\*\']? # optional nose

[:;=8] # eyes

[<>]? # optional hat/brow

Potts emoticons

Dan Jurafsky

Extracting Features for Sentiment Classification

• How to handle negation
• I didn’t like this movie

vs

• I really like this movie
• Which words to use?
• Only adjectives
• All words
• All words turns out to work better, at least on this data

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Dan Jurafsky

Negation

Add NOT_ to every word between negation and following punctuation:

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didn’t like this movie , but I

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didn’t NOT_like NOT_this NOT_movie but I

Das, Sanjiv and Mike Chen. 2001. Yahoo! for Amazon: Extracting market sentiment from stock message boards. In Proceedings of the Asia Pacific Finance Association Annual Conference (APFA).

Bo Pang, Lillian Lee, and Shivakumar Vaithyanathan. 2002. Thumbs up? Sentiment Classification using Machine Learning Techniques. EMNLP-2002, 79—86.

Dan Jurafsky

Reminder: Naïve Bayes

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Dan Jurafsky

Binarized (Boolean feature) Multinomial Naïve Bayes

• Intuition:
• For sentiment (and probably for other text classification domains)
• Word occurrence may matter more than word frequency
• The occurrence of the word fantastic tells us a lot
• The fact that it occurs 5 times may not tell us much more.
• Boolean Multinomial Naïve Bayes
• Clips all the word counts in each document at 1

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Dan Jurafsky

Boolean Multinomial Naïve Bayes: Learning

• Calculate P(c_j) terms
• For each c_j in C do

docs_j ← all docs with class =c_j

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• From training corpus, extract Vocabulary

• Calculate P(w_k | c_j) terms

• Remove duplicates in each doc:
• For each word type w in doc_j
• Retain only a single instance of w

Dan Jurafsky

Boolean Multinomial Naïve Bayes� on a test document d

• First remove all duplicate words from d
• Then compute NB using the same equation:

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Dan Jurafsky

Normal vs. Boolean Multinomial NB

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Dan Jurafsky

Binarized (Boolean feature) �Multinomial Naïve Bayes

• Binary seems to work better than full word counts
• This is not the same as Multivariate Bernoulli Naïve Bayes
• MBNB doesn’t work well for sentiment or other text tasks
• Other possibility: log(freq(w))

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B. Pang, L. Lee, and S. Vaithyanathan. 2002. Thumbs up? Sentiment Classification using Machine Learning Techniques. EMNLP-2002, 79—86.

V. Metsis, I. Androutsopoulos, G. Paliouras. 2006. Spam Filtering with Naive Bayes – Which Naive Bayes? CEAS 2006 - Third Conference on Email and Anti-Spam.

K.-M. Schneider. 2004. On word frequency information and negative evidence in Naive Bayes text classification. ICANLP, 474-485.

JD Rennie, L Shih, J Teevan. 2003. Tackling the poor assumptions of naive bayes text classifiers. ICML 2003

Dan Jurafsky

Cross-Validation

• Break up data into 10 folds
• (Equal positive and negative inside each fold?)
• For each fold
• Choose the fold as a temporary test set
• Train on 9 folds, compute performance on the test fold
• Report average performance of the 10 runs

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Dan Jurafsky

Other issues in Classification

• MaxEnt and SVM tend to do better than Naïve Bayes

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Dan Jurafsky

Problems: �What makes reviews hard to classify?

• Subtlety:
• Perfume review in Perfumes: the Guide:
• “If you are reading this because it is your darling fragrance, please wear it at home exclusively, and tape the windows shut.”
• Dorothy Parker on Katherine Hepburn
• “She runs the gamut of emotions from A to B”

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Dan Jurafsky

Thwarted Expectations�and Ordering Effects

• “This film should be brilliant. It sounds like a great plot, the actors are first grade, and the supporting cast is good as well, and Stallone is attempting to deliver a good performance. However, it can’t hold up.”
• Well as usual Keanu Reeves is nothing special, but surprisingly, the very talented Laurence Fishbourne is not so good either, I was surprised.

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Dan Jurafsky

Sentiment Analysis

A Baseline Algorithm

Dan Jurafsky

Sentiment Analysis

Sentiment Lexicons

Dan Jurafsky

The General Inquirer

• Home page: http://www.wjh.harvard.edu/~inquirer
• List of Categories: http://www.wjh.harvard.edu/~inquirer/homecat.htm
• Spreadsheet: http://www.wjh.harvard.edu/~inquirer/inquirerbasic.xls
• Categories:
• Positiv (1915 words) and Negativ (2291 words)
• Strong vs Weak, Active vs Passive, Overstated versus Understated
• Pleasure, Pain, Virtue, Vice, Motivation, Cognitive Orientation, etc
• Free for Research Use

Philip J. Stone, Dexter C Dunphy, Marshall S. Smith, Daniel M. Ogilvie. 1966. The General Inquirer: A Computer Approach to Content Analysis. MIT Press

Dan Jurafsky

LIWC (Linguistic Inquiry and Word Count)

Pennebaker, J.W., Booth, R.J., & Francis, M.E. (2007). Linguistic Inquiry and Word Count: LIWC 2007. Austin, TX

• Home page: http://www.liwc.net/
• 2300 words, >70 classes
• Affective Processes
• negative emotion (bad, weird, hate, problem, tough)
• positive emotion (love, nice, sweet)
• Cognitive Processes
• Tentative (maybe, perhaps, guess), Inhibition (block, constraint)
• Pronouns, Negation (no, never), Quantifiers (few, many)
• $30 or $90 fee

Dan Jurafsky

MPQA Subjectivity Cues Lexicon

• Home page: http://www.cs.pitt.edu/mpqa/subj_lexicon.html
• 6885 words from 8221 lemmas
• 2718 positive
• 4912 negative
• Each word annotated for intensity (strong, weak)
• GNU GPL

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Theresa Wilson, Janyce Wiebe, and Paul Hoffmann (2005). Recognizing Contextual Polarity in

Phrase-Level Sentiment Analysis. Proc. of HLT-EMNLP-2005.

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Riloff and Wiebe (2003). Learning extraction patterns for subjective expressions. EMNLP-2003.

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Dan Jurafsky

Bing Liu Opinion Lexicon

• Bing Liu's Page on Opinion Mining
• http://www.cs.uic.edu/~liub/FBS/opinion-lexicon-English.rar

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• 6786 words
• 2006 positive
• 4783 negative

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Minqing Hu and Bing Liu. Mining and Summarizing Customer Reviews. ACM SIGKDD-2004.

Dan Jurafsky

SentiWordNet

Stefano Baccianella, Andrea Esuli, and Fabrizio Sebastiani. 2010 SENTIWORDNET 3.0: An Enhanced Lexical Resource for Sentiment Analysis and Opinion Mining. LREC-2010

• Home page: http://sentiwordnet.isti.cnr.it/
• All WordNet synsets automatically annotated for degrees of positivity, negativity, and neutrality/objectiveness
• [estimable(J,3)] “may be computed or estimated”

Pos 0 Neg 0 Obj 1

• [estimable(J,1)] “deserving of respect or high regard”

Pos .75 Neg 0 Obj .25

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Dan Jurafsky

Disagreements between polarity lexicons

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Christopher Potts, Sentiment Tutorial, 2011

Dan Jurafsky

Analyzing the polarity of each word in IMDB

• How likely is each word to appear in each sentiment class?
• Count(“bad”) in 1-star, 2-star, 3-star, etc.
• But can’t use raw counts:
• Instead, likelihood:

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• Make them comparable between words
• Scaled likelihood:

Potts, Christopher. 2011. On the negativity of negation. SALT 20, 636-659.

Dan Jurafsky

Analyzing the polarity of each word in IMDB

Scaled likelihood

P(w|c)/P(w)

Scaled likelihood

P(w|c)/P(w)

Potts, Christopher. 2011. On the negativity of negation. SALT 20, 636-659.

Dan Jurafsky

Other sentiment feature: Logical negation

• Is logical negation (no, not) associated with negative sentiment?
• Potts experiment:
• Count negation (not, n’t, no, never) in online reviews
• Regress against the review rating

Potts, Christopher. 2011. On the negativity of negation. SALT 20, 636-659.

Dan Jurafsky

Potts 2011 Results:�More negation in negative sentiment

a

Scaled likelihood

P(w|c)/P(w)

Dan Jurafsky

Sentiment Analysis

Sentiment Lexicons

Dan Jurafsky

Sentiment Analysis

Learning Sentiment Lexicons

Dan Jurafsky

Semi-supervised learning of lexicons

• Use a small amount of information
• A few labeled examples
• A few hand-built patterns
• To bootstrap a lexicon

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Dan Jurafsky

Hatzivassiloglou and McKeown intuition for identifying word polarity

• Adjectives conjoined by “and” have same polarity
• Fair and legitimate, corrupt and brutal
• *fair and brutal, *corrupt and legitimate
• Adjectives conjoined by “but” do not
• fair but brutal

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Vasileios Hatzivassiloglou and Kathleen R. McKeown. 1997. Predicting the Semantic Orientation of Adjectives. ACL, 174–181

Dan Jurafsky

Hatzivassiloglou & McKeown 1997�Step 1

• Label seed set of 1336 adjectives (all >20 in 21 million word WSJ corpus)
• 657 positive
• adequate central clever famous intelligent remarkable reputed sensitive slender thriving…
• 679 negative
• contagious drunken ignorant lanky listless primitive strident troublesome unresolved unsuspecting…

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Dan Jurafsky

Hatzivassiloglou & McKeown 1997�Step 2

• Expand seed set to conjoined adjectives

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nice, helpful

nice, classy

Dan Jurafsky

Hatzivassiloglou & McKeown 1997�Step 3

• Supervised classifier assigns “polarity similarity” to each word pair, resulting in graph:

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classy

nice

helpful

fair

brutal

irrational

corrupt

Dan Jurafsky

Hatzivassiloglou & McKeown 1997�Step 4

• Clustering for partitioning the graph into two

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classy

nice

helpful

fair

brutal

irrational

corrupt

+

-

Dan Jurafsky

Output polarity lexicon

• Positive
• bold decisive disturbing generous good honest important large mature patient peaceful positive proud sound stimulating straightforward strange talented vigorous witty…
• Negative
• ambiguous cautious cynical evasive harmful hypocritical inefficient insecure irrational irresponsible minor outspoken pleasant reckless risky selfish tedious unsupported vulnerable wasteful…

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Dan Jurafsky

Output polarity lexicon

• Positive
• bold decisive disturbing generous good honest important large mature patient peaceful positive proud sound stimulating straightforward strange talented vigorous witty…
• Negative
• ambiguous cautious cynical evasive harmful hypocritical inefficient insecure irrational irresponsible minor outspoken pleasant reckless risky selfish tedious unsupported vulnerable wasteful…

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Dan Jurafsky

Turney Algorithm

1. Extract a phrasal lexicon from reviews
2. Learn polarity of each phrase
3. Rate a review by the average polarity of its phrases

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Turney (2002): Thumbs Up or Thumbs Down? Semantic Orientation Applied to Unsupervised Classification of Reviews

Dan Jurafsky

Extract two-word phrases with adjectives

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Dan Jurafsky

How to measure polarity of a phrase?

• Positive phrases co-occur more with “excellent”
• Negative phrases co-occur more with “poor”
• But how to measure co-occurrence?

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Dan Jurafsky

Pointwise Mutual Information

• Mutual information between 2 random variables X and Y

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• Pointwise mutual information:
• How much more do events x and y co-occur than if they were independent?

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Dan Jurafsky

Pointwise Mutual Information

• Pointwise mutual information:
• How much more do events x and y co-occur than if they were independent?

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• PMI between two words:
• How much more do two words co-occur than if they were independent?

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Dan Jurafsky

How to Estimate Pointwise Mutual Information

• Query search engine (Altavista)
• P(word) estimated by hits(word)/N
• P(word₁,word₂) by hits(word1 NEAR word2)/N²

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Dan Jurafsky

Does phrase appear more with “poor” or “excellent”?

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Dan Jurafsky

Phrases from a thumbs-up review

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Dan Jurafsky

Phrases from a thumbs-down review

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Dan Jurafsky

Results of Turney algorithm

• 410 reviews from Epinions
• 170 (41%) negative
• 240 (59%) positive
• Majority class baseline: 59%
• Turney algorithm: 74%

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• Phrases rather than words
• Learns domain-specific information

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Dan Jurafsky

Using WordNet to learn polarity

• WordNet: online thesaurus (covered in later lecture).
• Create positive (“good”) and negative seed-words (“terrible”)
• Find Synonyms and Antonyms
• Positive Set: Add synonyms of positive words (“well”) and antonyms of negative words
• Negative Set: Add synonyms of negative words (“awful”) and antonyms of positive words (”evil”)
• Repeat, following chains of synonyms
• Filter

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S.M. Kim and E. Hovy. 2004. Determining the sentiment of opinions. COLING 2004

M. Hu and B. Liu. Mining and summarizing customer reviews. In Proceedings of KDD, 2004

Dan Jurafsky

Summary on Learning Lexicons

• Advantages:
• Can be domain-specific
• Can be more robust (more words)
• Intuition
• Start with a seed set of words (‘good’, ‘poor’)
• Find other words that have similar polarity:
• Using “and” and “but”
• Using words that occur nearby in the same document
• Using WordNet synonyms and antonyms

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• Use seeds and semi-supervised learning to induce lexicons

Dan Jurafsky

Sentiment Analysis

Learning Sentiment Lexicons

Dan Jurafsky

Sentiment Analysis

Other Sentiment Tasks

Dan Jurafsky

Finding sentiment of a sentence

• Important for finding aspects or attributes
• Target of sentiment

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• The food was great but the service was awful

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Dan Jurafsky

Finding aspect/attribute/target of sentiment

• Frequent phrases + rules
• Find all highly frequent phrases across reviews (“fish tacos”)
• Filter by rules like “occurs right after sentiment word”
• “…great fish tacos” means fish tacos a likely aspect

M. Hu and B. Liu. 2004. Mining and summarizing customer reviews. In Proceedings of KDD.

S. Blair-Goldensohn, K. Hannan, R. McDonald, T. Neylon, G. Reis, and J. Reynar. 2008. Building a Sentiment Summarizer for Local Service Reviews. WWW Workshop.

Dan Jurafsky

Finding aspect/attribute/target of sentiment

• The aspect name may not be in the sentence
• For restaurants/hotels, aspects are well-understood
• Supervised classification
• Hand-label a small corpus of restaurant review sentences with aspect
• food, décor, service, value, NONE
• Train a classifier to assign an aspect to a sentence
• “Given this sentence, is the aspect food, décor, service, value, or NONE”

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Dan Jurafsky

Putting it all together:�Finding sentiment for aspects

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Reviews

Final

Summary

Sentences

& Phrases

Sentences

& Phrases

Sentences

& Phrases

Text

Extractor

Sentiment

Classifier

Aspect

Extractor

Aggregator

S. Blair-Goldensohn, K. Hannan, R. McDonald, T. Neylon, G. Reis, and J. Reynar. 2008. Building a Sentiment Summarizer for Local Service Reviews. WWW Workshop

Dan Jurafsky

Results of Blair-Goldensohn et al. method

Rooms (3/5 stars, 41 comments)

(+) The room was clean and everything worked fine – even the water pressure ...

(+) We went because of the free room and was pleasantly pleased ...

(-) …the worst hotel I had ever stayed at ...

Service (3/5 stars, 31 comments)

(+) Upon checking out another couple was checking early due to a problem ...

(+) Every single hotel staff member treated us great and answered every ...

(-) The food is cold and the service gives new meaning to SLOW.

Dining (3/5 stars, 18 comments)

(+) our favorite place to stay in biloxi.the food is great also the service ...

(+) Offer of free buffet for joining the Play

Dan Jurafsky

Baseline methods assume classes have equal frequencies!

• If not balanced (common in the real world)
• can’t use accuracies as an evaluation
• need to use F-scores
• Severe imbalancing also can degrade classifier performance
• Two common solutions:
1. Resampling in training
• Random undersampling
2. Cost-sensitive learning
• Penalize SVM more for misclassification of the rare thing

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Dan Jurafsky

How to deal with 7 stars?

1. Map to binary
2. Use linear or ordinal regression
• Or specialized models like metric labeling

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Bo Pang and Lillian Lee. 2005. Seeing stars: Exploiting class relationships for sentiment categorization with respect to rating scales. ACL, 115–124

Dan Jurafsky

Summary on Sentiment

• Generally modeled as classification or regression task
• predict a binary or ordinal label
• Features:
• Negation is important
• Using all words (in naïve bayes) works well for some tasks
• Finding subsets of words may help in other tasks
• Hand-built polarity lexicons
• Use seeds and semi-supervised learning to induce lexicons

Dan Jurafsky

Scherer Typology of Affective States

• Emotion: brief organically synchronized … evaluation of a major event
• angry, sad, joyful, fearful, ashamed, proud, elated
• Mood: diffuse non-caused low-intensity long-duration change in subjective feeling
• cheerful, gloomy, irritable, listless, depressed, buoyant
• Interpersonal stances: affective stance toward another person in a specific interaction
• friendly, flirtatious, distant, cold, warm, supportive, contemptuous
• Attitudes: enduring, affectively colored beliefs, dispositions towards objects or persons
• liking, loving, hating, valuing, desiring
• Personality traits: stable personality dispositions and typical behavior tendencies
• nervous, anxious, reckless, morose, hostile, jealous

Dan Jurafsky

Computational work on other affective states

• Emotion:
• Detecting annoyed callers to dialogue system
• Detecting confused/frustrated versus confident students
• Mood:
• Finding traumatized or depressed writers
• Interpersonal stances:
• Detection of flirtation or friendliness in conversations
• Personality traits:
• Detection of extroverts

Dan Jurafsky

Detection of Friendliness

• Friendly speakers use collaborative conversational style
• Laughter
• Less use of negative emotional words
• More sympathy
• That’s too bad I’m sorry to hear that
• More agreement
• I think so too
• Less hedges
• kind of sort of a little …

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Ranganath, Jurafsky, McFarland

Dan Jurafsky

Sentiment Analysis

Other Sentiment Tasks

Dan Jurafsky