Perception problems of the verbal scale: A reanalysis and application of a membership function approach

Verbal conclusion scales provide a standardized vocabulary that forensic scientists can adopt to describe the amount of support offered by a set of observations with regard to two competing hypotheses. The extent to which these verbal scales can efficiently and accurately communicate strength of support to lay evaluators is, however, an empirical matter of considerable importance. The aim of this paper was to reexamine the results of a recent study measuring lay interpretations of expert verbal phrases (Mullen et al., 2014) and to further improve upon those estimates through the utilization of a membership function approach. Across both the reexamination (n = 400) and the new experiment (n = 134) 534 participants provided translations of expert verbal conclusion scales used by forensic scientists. Overall, there is compelling evidence that the correspondence between expert intentions and lay interpretations is low, while the potential for miscommunication is high. Consequently, further attention is required to facilitate the development of valid and reliable verbal conclusion scales which clearly communicate expert evaluative opinions.