風險下決策的稟賦效果隨受擁有感受而增強

Abstract

稟賦效果（endowment effect）指出對於一個物品的偏好會因為擁有它而提升。過去研究顯示當擁有一張帶有不確定性的彩券(lottery)時，稟賦效果會降低。另一方面，越來越多研究指出心理上的擁有感受（psychological ownership）才是造成稟賦效果的原因。然而亦有研究指出，擁有感受的高低會受到擁有物品性質的影響。因此，稟賦效果是否受到機率或其他因素影響仍有待解決。本研究主要探討心理上的擁有感受如何調節選項屬性，進而影響選擇的偏好。30位參與者（15位女性）進行總計72回合(trial)的多次二選項強迫選擇測驗（two-alternative forced-choice）。兩個選項分別為「擁有彩券」與「新彩券」。回合初始，參與者會先擁有一張被分派（Assigned）的彩券，接著會出現另一張與被分派彩券在中獎機率與金額上皆有差異的新彩券，受試必須在兩張彩卷中做出選擇，被選擇的彩券會成為同一回合中下次選擇的擁有彩券。根據受試獲得彩卷的方式，擁有彩券可以透過分派（Assigned）與選擇（Chosen）兩種方式獲得。實驗結果顯示，一、心理上的擁有感受會提升稟賦效果；二、心理上擁有感受的效果，會受到擁有彩券相對風險程度調節；三、選項間屬性（中獎機率與金額）的差異或平均愈大，參與者的選擇受到該屬性的影響也會愈大；四、相對於新彩券，擁有彩券增強該選擇之優勢屬性權重及弱化劣勢屬性權重，而且此效果會因擁有感增強而放大。總括來說，在風險下決策的情況，心理上的擁有感受會透過調節各個相對屬性對決策的影響，放大擁有彩券的優勢以產生更強烈的稟賦效果。

The endowment effect is a tendency to value a good more when owning it. The size of the endowment effect was affected by the reward probability of the owning lottery. By country, it was also found that the preference for a good was not affected by the owning probability. Growing evidence also supported that psychological ownership could enhance the endowment effect. However, it was found that the sense of ownership might be modulated by the good’s attributes. Thus, whether the endowment effect was influenced by reward probability or not remained an open question. In this study, we investigated the influence of lottery attributes on endowment effect under different levels of psychological ownership. Thirty subjects (15 females) carried out 72 trials of sequential two-alternative forced-choice between an owned lottery and a new. Psychological ownership of the owned was manipulated by the source of receiving. The new was a lottery that differed from the owned in both reward probability and reward magnitude. Here we reported four main findings. First, psychological ownership of the owned lottery increased the keeping tendency. Second, the influence of the psychological ownership was regulated by the relative riskiness of the owned lottery. Third, both mean and difference on each attribute (probability or reward) between options increased the weighting of that attribute on the decision. Fourth, psychological ownership enhanced the influence of the attribute difference in which the owned lottery was higher than the new, and decreased the influence of the attribute difference in which the owned lottery was lower. In summary, we found that a greater sense of ownership on a risky endowment enhanced the endowment effect through the biased weighting on each relative attribute to enlarge the preference for the owned option.