The application of multinomial models in moral judgment research

Morality has been a hot topic in the psychological literature, and moral judgment, appraising process that enables individuals to differentiate good from evil and right from wrong according to moral principles, is a critical component of human morality. This review aims to introduce the application of multinomial models in moral judgment research. Several theories have been proposed to explain how moral judgment is made. Dual-process theory of moral judgment proposed that moral judgment is shaped by two moral principles (i.e., utilitarianism and deontology). The principle of utilitarianism emphasizes that the morality of an action is determined by its consequence whereas the principle of deontology states that the morality of an action depends on its consistency with moral norms. To measure people's moral inclinations in moral judgment, researchers developed moral dilemma paradigm that pit the utilitarian principle against the deontological principle. Based on this moral dilemma paradigm, moral psychologists have revealed gender difference (i.e., men are more utilitarian) and individual differences (e.g., psychopathy individuals are more utilitarian) in moral judgment. However, the traditional moral dilemma paradigms, which did not distinguish the consequences and moral norms in moral dilemmas, can't precisely measure an individual's inclinations to utilitarian and deontological nor preclude potential confounders (e.g., people's preference to act or not in moral dilemmas). To overcome these shortcomings of the traditional moral dilemma paradigms, researchers have recently developed a multinomial model (i.e., the CNI model) that allows researchers to quantify sensitivity to consequences (C), sensitivity to moral norms (N), and a general preference for inaction versus action irrespective of consequences and norms (I) in responses to moral dilemmas. This review aims to discuss the disadvantages of traditional moral dilemma paradigm and the advantages of the CNI model, and to summarize how CNI model-based findings contribute to our understanding of moral judgment. Specifically, recent work based on the CNI model of moral judgment has elaborated on how cognitive load and incidental happiness affect specific psychological processes of moral judgment, which challenges the dual-process theory of moral judgment. Moreover, the cognitive mechanisms underlying the individual differences (i.e., gender and psychopathy) in moral judgment have been clarified. We also point out future directions for moral judgment research. First, due to a small number of observation data in the model (i.e., data from only 24 moral dilemmas), the CNI model may not fit the data well at an individual-level and thus not be suitable for correlational designs. Future studies need to develop a larger set of moral dilemmas to increase the observations for the model and allow model fitting at an individual level. Second, it has been recognized that Chinese people showed stronger deontological inclination than British people, thus it would be interesting to uncover the underlying neurocognitive mechanism of culture differences in moral judgment. Third, several neuromodulators, such as oxytocin and serotonin, have been shown to affect moral judgment, future research is thus needed to clarify the influence of neuromodulators on specific cognitive processes underlying moral preferences. In conclusion, this review highlights the advantages of multinomial modeling and summarizes how the CNI model-based findings deepen our understanding of moral judgment, and the individual differences (i.e., gender and psychopathy) in moral judgment, which yields insights into human morality.