The expression of uncertainty: Two contextual effects

Abstract

Since Foley (1959), the technique of evaluating common expressions of uncertainty on a numerical scale has often been used in an attempt to define such expressions more accurately. Two contextual factors - (1) the composition of the set of expressions and (2) the definition of the scale - were studied in the present experiment to determine their effect on bow such expressions are encoded. Psychophysical theories on series effects and, in particular, the range-frequency model (Parducci, 1983), predict that the composition of a set is one of the determining factors of contrast effects. The scale definition factor determines the lower limit of the rating scale, which represents either uncertainty or negative certainty. The effect of this factor is assumed to depend upon the reference universe outlined in the problem statement and, in particular, upon whether that universe is strictly limited or not. An experiment was conducted to contrast two sets of expressions, two scale definitions and two ways of presenting the problem (the doubt was applied either to a choice of two events or to the occurrence of an event in an unspecified universe). The results provide evidence of a set composition effect and an interaction between the scale definition and the presentation of the problem. This is consistent with the proposed model, which accounts for the specific effects of the judgement task while eliminating the need to consider the variability of the meanings themselves. Proposals for developing this line of research are presented in the discussion.