The influence of variables in product spaces

Jean Bourgain*, Jeff Kahn, Gil Kalai, Yitzhak Katznelson, Nathan Linial

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

98 Scopus citations


Let X be a probability space and let f: X n → {0, 1} be a measurable map. Define the influence of the k-th variable on f, denoted by I f (k), as follows: For u=(u 1, u 2,..., u n-1) ∈X n-1 consider the set l k (u)={(u 1, u 2,..., u k-1, t, u k,..., u n-1):t ∈X}. {Mathematical expression} More generally, for S a subset of [n]={1,..., n} let the influence of S on f, denoted by I f (S), be the probability that assigning values to the variables not in S at random, the value of f is undetermined. Theorem 1:There is an absolute constant c 1 so that for every function f: X n → {0, 1}, with Pr(f -1(1))=p≤1/2, there is a variable k so that {Mathematical expression} Theorem 2:For every f: X n → {0, 1}, with Prob(f=1)=1/2, and every ε>0, there is S ⊂ [n], |S|=c 2(ε)n/log n so that I f (S)≥1-ε. These extend previous results by Kahn, Kalai and Linial for Boolean functions, i.e., the case X={0, 1}.

Original languageAmerican English
Pages (from-to)55-64
Number of pages10
JournalIsrael Journal of Mathematics
Issue number1-2
StatePublished - Feb 1992


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