A noncentral distribution is a member of a family of sampling distributions obtained when the statistic underlying a central distribution is formed from variables having nonzero means. The resulting noncentrality parameter measures the departure from the null value, and setting it equal to 0 recovers the corresponding central distribution.
Important examples are the noncentral chi-squared distribution, the noncentral F-distribution, and the noncentral Student's t-distribution. These distributions arise naturally in power calculations for hypothesis tests.
