sentiment

Semisupervised learning to induce lexicons sentiment

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Unformatted text preview: ents x and y co ­occur than if they were independent? PMI( X, Y ) = log 2 P( x, y) P ( x )P ( y ) Dan Jurafsky Pointwise Mutual Informa%on •  Pointwise mutual informa%on: •  How much more do events x and y co ­occur than if they were independent? P( x, y) PMI( X, Y ) = log 2 P ( x )P ( y ) •  PMI between two words: •  How much more do two words co ­occur than if they were independent? P(word1,word2 ) PMI(word1, word2 ) = log 2 P(word1)P(word2 ) Dan Jurafsky How to Es%mate Pointwise Mutual Informa%on •  Query search engine (Altavista) •  P(word) es+mated by hits(word)/N! •  P(word1,word2) by hits(word1 NEAR word2)/N2! hits(word1 NEAR word2 ) PMI(word1, word2 ) = log 2 hits(word1)hits(word2 ) Dan Jurafsky Does phrase appear more with “poor” or “excellent”? Polarity( phrase) = PMI( phrase, "excellent") ! PMI( phrase, "poor") hits(phrase NEAR "excellent") hits(phrase NEAR "poor") = log 2 ! log 2 hits(phrase)hits("excellent") hits(phrase)hits("poor") hits(phrase NEAR "excellent") hits(phrase)hits("poor") = log 2 hits(phrase)hits("excellent") hits(phrase NEAR "poor") 62 ! hits(phrase NEAR "excellent")hits("poor") $ = log 2 # & " hits(phrase NEAR "poor")hits("excellent") % Dan Jurafsky Phrases from a thumbs ­up review Phrase POS tags Polarity online service JJ NN 2.8! online experience JJ NN 2.3! direct deposit JJ NN 1.3! local branch JJ NN 0.42! low fees JJ NNS 0.33! true service JJ NN -0.73! other bank JJ NN -0.85! inconveniently located JJ NN -1.5! … 63 Average 0.32! Dan Jurafsky Phrases from a thumbs ­down review Phrase POS tags Polarity direct deposits JJ NNS 5.8! online web JJ NN 1.9! very handy RB JJ 1.4! vir...
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