APA Dictionary of Psychology

n. a statistical procedure used to estimate the variability of a parameter associated with a set of data, such as the standard error or confidence interval. It is particularly appropriate when the variance or underlying distribution is not known. A number of samples are obtained from the original data by eliminating one or more observations at a time, the parameter in question is calculated for each sample, and the individual parameters are combined to provide an estimate of the overall parameter for the entire data set. A jackknife is similar to bootstrapping, except that bootstrapping involves replacing observations after they have been sampled, such that after each observation is chosen it is reinserted into the data for possible selection again.