Barbara George

Measurement uncertainty has long been a concern in the characterizing and interpreting environmental and toxicological measurements. We compared statistical analysis approaches when there are replicates: a Naı̈ve approach that omits replicates, a Hybrid approach that inappropriately treats replicates as independent samples, and a Measurement Error Model (MEM) approach in a random effects analysis of variance (ANOVA) model that appropriately incorporates replicates.

We appreciate the thoughtful commentary and opportunity to continue the discussion on this important topic of dealing with left-censored data. We thank Prof. Hites for reflecting on our introduction and want to reinforce that the challenges for measurement of trace-level environmental data and their statistical analysis are long-standing, complex, and continually evolving.

Trace-level environmental data typically include values near or below detection and quantitation thresholds where health effects may result from low-concentration exposures to one chemical over time or to multiple chemicals.