The geometric distribution describes the number of trials up to and including the first success, in independent trials with the same probability of success. The geometric distribution depends only on the single parameter p, the probability of success in each trial. For example, the number of times one must toss a fair coin until the first time the coin lands heads has a geometric distribution with parameter p = 50%. The geometric distribution assigns probability p×(1 − p)k⁻¹to the event that it takes k trials to the first success. The expected value of the geometric distribution is 1/p, and its SE is (1−p)^½/p.