Weight-of-Evidence Issues and Frameworks for Sediment Quality (And Other) Assessments

Weight of evidence (WOE) frameworks for integrating and interpreting multiple lines of evidence are discussed, focusing on sediment quality assessments, and introducing a series of ten papers on WOE. Approaches to WOE include individual lines of evidence (LOE) as well as combined LOE (indices, statistical summarization, logic systems, scoring systems, and best professional judgment [BPJ]). The application of WOE, based on multiple LOE, is discussed relative to the published literature. Fully implementing WOE requires consideration of six main LOE in sediment (or other assessments); these LOE generally correspond to other causality considerations including Koch's Postulates. However, the issue of sediment stability is an additional consideration, and the use of tabular decision matrices is recommended in a logic system to address LOE described by others as “analogy”, “plausibility”, or “logical and scientific sense.” Three examples of logic system WOE determinations based on the Sediment Quality Triad and using tabular decision matrices are provided. Key lessons from these examples include the: generally limited utility of sediment quality value (SQV)-based LOE; need for BPJ; importance of ecological relevance; importance of assessing background conditions; and, need for appropriately customizing study designs to suit sitespecific circumstances (rather than application of “boiler-plate” assessments). Overall, more quantitative approaches are needed that better define certainty elements of WOE in an open framework process, i.e., statistical summarization culminating in a logic system incorporating BPJ.     

Detection of Tastes in Mixture with Other Tastes: Issues of Masking and Aging

When one taste (masker) is strong enough, it can completelymask another taste (target) of different quality. How strongthe masker must be to do this depends on how strong the targetis. As the target concentration is increased, the masking concentrationmust be increased, too, but in ever-increasing proportion. Toquantify the conditions for such complete masking, the target'sdetection threshold was measured as a function of the masker'sconcentration, from zero to strong. This was done for 12 binarycombinations of sucrose, sodium chloride, citric acid and quininehydrochloride. The 12 functions generated show that some tastantsmask each other much more efficiently than others. Masking givesnew insight into the role of aging in taste: older (66–90years) subjects' thresholds, regardless of masking concentration,always measured a constant factor higher than younger (18–29years) subjects' thresholds (about two to seven times higher,depending on target tastant). Thus, with increasing level ofthe masker, the thresholds of young and elderly go up in parallel.Thresholds of tastants in water alone are false predictors ofelderly persons' ability to perceive ingredients like salt andsugar condiments in foods, where, because of masking, theirthresholds can be several times higher than in water. Age manifesteditself relatively mildly in sucrose and citric acid, moderatelyin sodium chloride, and strongly in quinine hydrochloride. Chem.Senses 21: 211–221, 1996.