The underlying intuition known as distributional hypothesis (Harris, 1954) can be summarized as: "a word is characterized by the company it keeps" (Firth, 1957).
corr (P (c = 1, Y = 1) − P (c = 1)P (Y = 1)) 2 P (Y = 1)(P (Y = 0))V ar(P (c = 1|X)) In the equation, the term (P (c = 1, Y = 1) − P (c = 1)P (Y = 1)) 2 describes the dependency between context feature c and the class label Y .