A function of the observations having a distribution that does not depend on any parameter other than the parameter of interest. For example, if a random sample of n observations is taken from a normal distribution with unknown mean μ and variance σ² then a pivotal quantity for the parameter μ is the statistic t, given bywhere x̄ is the sample mean and s² is the sample variance (calculated using the (n−1) divisor). The distribution of t (a t-distribution with (n−1) degrees of freedom) does not depend on the value of σ².