Cumulative distribution function (CDF)

The probability that a device will have failed by a specified time t₁, or the fraction of units that have failed by that time. The value of this function is given by the integral of the probability density function, f(t), from t = 0 to t = t₁ and is generally expressed in percent (%) or in parts per million (ppm) for a defined early-life failure period. The abbreviation CDF is often used; however, the symbol F(t) is preferred.