Journal Article

More Than Obvious: Better Methods for Interpreting Nondetect Data

Low-level concentrations of organic andinorganic chemicals are often reportedas “nondetect” or “less-than” values.These concentrations are known only tobe somewhere between zero and the laboratory'sreporting level (RL). Fifteen years ago, ES&Tpublished an article titled “Less Than Obvious” (1)that outlined methods for the statistical analysis ofnondetect data. Since that time, the fields of survivalanalysis and reliability analysis (2, 3) have continuedto improve on methods for handling censoreddata—those observations reported only as beingabove or below a threshold value. For example,methods for hypothesis tests and regression for censoreddata are now standard features of statisticssoftware. Decades-old methods in these two fieldsthat were originally applied only to “greater thans”can also be applied to the “less thans” of low-levelenvironmental concentrations.

Publisher - American Chemical Society

Subjects - Nondetect Data; Statistics

Citation: Helsel D. 2005. More Than Obvious: Better Methods for Interpreting Nondetect Data. Environ. Sci. Technol.; 39(20):419A-423A