Tatsuya Kameda

The Robust Beauty of Majority Rules in Group Decisions

How should groups make decisions? The authors provide an original evaluation of 9 group decision rules based on their adaptive success in a simulated test bed environment. When the adaptive success standard is applied, the majority and plurality rules fare quite well, performing at levels comparable to much more resource-demanding rules such as an individual judgment averaging rule. The plurality rule matches the computationally demanding Condorcet majority winner that is standard in evaluations of preferential choice. The authors also test the results from their theoretical analysis in a behavioral study of nominal human group decisions, and the essential findings are confirmed empirically. The conclusions of the present analysis support the popularity of majority and plurality rules in truth-seeking group decisions.

'Social Sharedness' as a Unifying Theme for Information Processing in Groups

Although much of the research on small groups in social psychology has emphasized cognitive, information-processing tasks (decision-making and problem solving), only recently have groups been conceptualized as information-processing systems. Partially due to this new conceptualization, group research is on the rise, yet much of this research is discipline specific. Few attempts have been made to integrate this research to provide common themes or frameworks across disciplinary boundaries. We propose that one potential unifying theme underlying much of the recent research on groups is ‘social sharedness’: the degree to which cognitions, preferences, identities, etc. are shared and are being shared within groups. Through a targeted review of the literature, we attempt to demonstrate that social sharedness is central to understanding group decision-making, provides a tie between past and current group research, and can serve a unifying function for future endeavors.

The Logic of Social Sharing: An Evolutionary Game Analysis of Adaptive Norm Development

Although norms can potentially serve useful constructs to understand human minds, being fundamentally social in evolutionary as well as cultural senses, there are as yet no useful psychological theories of adaptive norm development. This article provides an illustrative model about how a norm emerges in a society. We focus on the “communal-sharing norm” in primordial societies, a norm designating uncertain resources as common properties to be shared with other members. Based on anthropologicalfindings, we develop a theory about how the communal-sharing norm emerges and is maintained. Then, using evolutionary computer simulations, we test several hypotheses about the conditions under which the norm will dominate social resource sharing. We further test behavioral implications of the norm, demonstrating that uncertainty involved in resource acquisition is a key factor that triggers the psychology of sharing even in highly industrialized societies. Finally, we discuss the importance of norm construct for analyzing the dynamic relation between minds and society.

Social sharing and risk reduction : Exploring a computational algorithm for the psychology of windfall gains

Sharing important resources widely beyond direct kin group members is one of the core features characterizing human societies. Moreover, generalized exchange involving many community members (e.g., meat sharing in bands) seems to be a uniquely human practice. This paper explores a computational algorithm for the psychology of social sharing that may underlie such practices, based on the risk-reduction hypothesis in food sharing of Kaplan and Hill [Curr. Anthropol. 26 (1985) 223]. We predicted that, independent of the amount of effort actually invested, uncertainty involved in resource acquisition is a key factor that triggers the psychology of social sharing for both acquirers and nonacquirers of a resource. It was also predicted that the ‘‘windfall effect’’ is independent of individual preferences as to modern distributive ideologies. Four multisample/multimethod studies, using Japanese and American participants, and laboratory as well as vignette experiments, supported these predictions: although the identical fungible resource (money) was under consideration, different psychological processes were triggered, depending on the degree of uncertainty involved in the money acquisition. Implications of the windfall effect for egalitarianism in resource sharing, observed not only in

Emerging Perspectives on Judgment and Decision Research: Cognitions, Preferences, and Social Sharedness: Past, Present, and Future Directions in Group Decision Making

Research on group decision making has several distinctive roots in social sciences. Besides psychological and sociological interests about how people make decisions as a collective (e.g., Coleman, 1990; Witte & Davis, 1996), group decision making has also been a major research topic in the interdisciplinary area, called social choice theory, that intersects economics and political science (Arrow, 1963; Black, 1958; Fishburn, 1973; Ordeshook, 1986). Although these disciplines differ in many ways about how and on what to focus (e.g., empirical versus analytical emphasis, consensus versus choice), perhaps one of the most profound differences is how they characterize “legitimate” inputs for collective choices -what elements are regarded as justifiable inputs to render group decisions. In this chapter, we start with a discussion on this “legitimate input” issue. We then demonstrate that distinguishing two levels on inputs conceptually provides a useful overarching picture to synthesize our empirical knowledge about decision making in consensus groups. In so doing, we aim to show that a single most powerful determinant of actual consensus outcomes may be “social sharedness,” the degree of knowledge sharing among people, at both levels of social aggregation.

Evolution, culture, and the human mind

omething extraordinary happened on the evolutionary path that gave rise to creatures capable of culture. The changes are so profound it is as if we humans were somehow domesticated. levels of violence are drastically lower than for the other great apes. We are born helpless, we require extended care, and we actively teach each other. We pay exquisite attention to each other’s wishes and emotional states. We not only cooperate in ways other great apes can--tic behaviors obviously harmful to fitness. even our bones are different from our ancestors in ways typical of a domesticated species (leach, 2003).domestication does not require planning. Self-interested behaviors are suffi-cient. Chasing away aggressive wolves allows friendly ones to gain an advantage by scavenging scraps. after only a thousand generations, this has transformed wolves into the prosocial, loyal, and helpful dogs we now love. Of course, humans were not domesticated by choices made by some other species. nonetheless, many human social characteristics would be easy to understand if we had somehow been domes-ticated. aspects of culture now select for prosociality and capacities for complex social cognition. But what happened before there was culture? What got the pro-cess going?We are understandably curious about what happened on our evolutionary path that made us capable of culture. The sequence likely involved so many interacting factors and recursive causal cycles that any description that satisfies our evolved minds will inevitably oversimplify the actual process. nonetheless, as illustrated by the chapters in this book, an enormous amount of thought and research has advanced our understanding of how selection shaped capacities for culture. Old arguments pitting evolution and culture as alternatives have been replaced by formulations that recognize both as essential to any full explanation of human

Effects of Assigned Group Consensus Requirement on Group Problem Solving and Group Members' Learning

This study investigated performance on mathematical problems by individuals and by groups working under one of three assigned consensus rules: majority, unanimity, or a no-consensus rule (discussion but no required consensus)

Some social mechanics of group decision making: The distribution of opinion, polling sequence, and implications for consensus.

The first study extrapolated earlier findings (Davis, Stasson, Ono, & Zimmerman, 1988) that the critical fourth voter in six-person mock juries evenly divided between guilty-and not-guilty-inclined jurors (3, 3) were significantly influenced by the preceding sequence (guilty or not-guilty faction voting first) and timing of a straw poll. Experiment 2 focused only on sequential voting in (4, 2) groups in which sequential voting by majority-minority factions first was again observed to influence critical individuals, although the effect was sharply mediated by the «leniency bias»

Interpersonal trust and social stress-induced cortisol elevation.

A neuroendocrine correlate of interpersonal trust is relatively unknown. We investigated the relationship between an interpersonal trust-related personality (General Trust Scale) and cortisol elevation induced by social stress in 20 men. Spearmans rank order correlation analysis revealed a significant negative correlation between social stress-induced cortisol elevation and General Trust Scale. The present results indicate subjects with higher degrees of interpersonal trust have lower levels of neuroendocrine response to social stress.

Democracy Under Uncertainty: The ‘Wisdom of Crowds’ and the Free-Rider Problem in Group Decision Making

We introduce a game theory model of individual decisions to cooperate by contributing personal resources to group decisions versus by free-riding on the contributions of other members. In contrast to most public-goods games that assume group returns are linear in individual contributions, the present model assumes decreasing marginal group production as a function of aggregate individual contributions. This diminishing marginal returns assumption is more realistic and generates starkly different predictions compared to the linear model. One important implication is that, under most conditions, there exist equilibria where some, but not all members of a group contribute, even with completely self-interested motives. An agent-based simulation confirms the individual and group advantages of the equilibria in which behavioral asymmetry emerges from a game structure that is a priori perfectly symmetric for all agents (all agents have the same payoff function and action space, but take different actions in equilibria). And a behavioral experiment demonstrates that cooperators and free-riders coexist in a stable manner in groups performing with the non-linear production function. A collateral result demonstrates that, compared to a – dictatorial decision scheme guided by the best member in a group, the majority-plurality decision rules can pool information effectively and produce greater individual net welfare at equilibrium, even if free-riding is not sanctioned. This is an original proof that cooperation in ad hoc decision-making groups can be understood in terms of self-interested motivations and that, despite the free-rider problem, majority-plurality decision rules can function robustly as simple, efficient social Democracy Under Uncertainty.