Commensurability in Decision Making

The thesis has established that commensurability encourages behavioural biases in decision making; moreover, incommensurability discourages behavioural biases in decision making. Commensurability is the proposal that two values can be placed on a single common dimension for comparison. In contrast, incommensurability dictates that two values or items cannot be placed on a single common dimension for comparison - incommensurable items cannot be compared. Recent theories of decision making have identified that comparative processes rather than calculative mechanisms underlie decision making. Moreover, these theories have sought to account for behavioural biases within the constraints of calculative processes. The current thesis has examined over eight experiments, the effect of commensurability and incommensurability on behavioural biases; establishing that preventing comparisons with incommensurability reduces decision makers propensity to display behavioural biases. The effect of commensurability/incommensurability on behavioural biases occurs, as commensurable decision tasks encourage decision makers to use biased comparative decision-making processes, whereas incommensurability discourages decision makers from using biased comparative processes. The ability for incommensurability to reduce behavioural biases has been established across three areas of decision making; risky decisions with loss aversion, multi-attribute choice and choice blindness. The first experimental chapter examined the impact of task commensurability on loss aversion by introducing incommensurability between the task (initial presentation of the gamble) and the judgement (evaluation of the gamble). Prevented comparisons with task commensurability between the two stages of the decision making task reduced the proportion of loss averse judgements made by decision makers. The second experimental chapter examined the effect of introducing incommensurability between choice options, preventing options from being compared, on the attraction and compromise effects. Introducing incommensurability between choice options reduced participants biases in exhibiting the attraction and compromise effects. Finally, the third experimental chapter utilised commensurability in exploration of the choice blindness phenomenon; introducing incommensurable choice options and also incommensurability between the initial decision and the secondary justification of the decision. Introducing both forms of incommensurability preventing comparative strategies from being used in the decision-making task, reduced the number of participants who exhibited choice blindness. Whilst various theoretical perspectives of decision making have touched on the role of commensurability or comparisons, the findings of this thesis stand in contrast to utilitarian theories of decision making, revealing that commensurability does not facilitate utilitarian decision making. Specifically, commensurability allows decision makers to integrate decision content, which leads to biases in decision making. Finally, regarding proposals of decision making founded on biased comparative decision-making process, the thesis offers the other half of the picture - preventing comparisons with incommensurability reduces behavioural biases.