The Bernoulli distribution, named after Swiss scientist James Bernoulli, is a discrete probability distribution, which takes value 1 with success probability p and value 0 with failure probability q = 1 − p. The probability mass function f of this distribution is

The expected value of a Bernoulli random variable is p, and its variance is pq = p(1 − p).

The Bernoulli distribution is a member of the exponential family.