[en] This paper reviews statistical procedures for estimating the mean μ and standard deviation (S.D.) σ of radionuclide data sets containing negative, unreported, or 'less-than' values resulting from concentrations being less than the analytical detection limit. Computational procedures leading to biased estimates are reviewed and alternate methods presented. The arithmetic mean, S.D. and median are compared with methods appropriate when the underlying distribution is lognormal and data sets are left-censored. (author)