Let X-1, ..., X-n be independent, not necessarily identically distributed r
andom variables. An optimal bound is derived for the concentration function
of an arbitrary real-valued statistic T = T (X-1,..., X-n) for which ET2 <
infinity. Applications are given for Wilcoxon's rank-sum statistic, U-stat
istics, Student's statistic, the two-sample Student statistic and linear re
gression.