Pointwise Mutual Information

=== do events x and y co-occur more than if they were independent?==

Formula

==$\mathrm{PMI}(X,Y)={\log }_2\frac{P(x,y)}{P(x)P(y)}$==

Problem:

• PMI ranges from -∞ to +∞
  • → co-occurrence LESS than we expect by chance (?!)
• unreliable with huge corpora
• Solution: Positive Pointwise Mutual Information