Multiwinner voting aims to select a subset of alternatives (a committee) from a larger set of admissible alternatives, according to the votes cast by voters. We consider in this paper that each voter is endowed with a preference order in which the alternatives are ranked from the best to the worst. In this setting, we can define committee scoring rules as multiwinner analogues of positional scoring rules which constitute a well-known subclass of single-winner voting rules. A special class of committee scoring rules – (weakly) separable scoring rules – have gained considerable attention recently. Under this class, when the aim is to select a committee of size exactly k, we can first compute a separate score for each alternative using a single-winner scoring rule and then pick the k alternatives with the top scores. When the underlying single-winner scoring rule does (not) depend on the size k of the target committee then the rule is referred to as (weakly) separable. In this paper, we consider a model of multiwinner voting using (weakly) separable scoring rules where, moreover, alternatives have certain attributes and for each attribute there is a minimal desired number that the selected committee should fit. In this setting, enforcing attribute constraints on the winning committee must naturally have a cost since the feasible space of committees becomes smaller and hence the optimal score may decrease. We measure this cost, that we refer to as the price of diversity, by considering the ratio between the score of the optimal unconstrained committee and the score of the optimal constrained committee. We study to what extent the price of diversity changes regarding the choosen rule.

Humans are a social species and many decisions we make are inherently driven by our social preferences. However, these decisions are frequently made in the presence of stressors, ranging from mild inconveniences, such as missing the bus, to severe events, such as the death of a loved one. Existing evidence regarding the effects of acute stress on social decision-making paint an inconsistent picture. These studies suffer from a male bias and do not control for baseline preferences. We experimentally investigate the effects of acute stress on social preferences, focusing on the moderating role of baseline social preferences and sex. Using a sex-balanced sample (N=271), we randomly assigned participants to either the stress or control (placebo stress) treatment. Participants underwent the (placebo) Maastricht Acute Stress Task and successful stress induction was evaluated through salivary cortisol and blood pressure. Distributional social preferences were elicited using a series of incentivized binary dictator games. Results indicate that stress-response-induced cortisol changes predict differences in social preferences, with stressed individuals exhibiting more selfish behaviors than their non-stressed counterparts. Interestingly, this effect appears to be driven primarily by individuals with low or no cortisol response displaying increases in prosocial behavior. Results further suggest that the cortisol effect is weaker for individuals with more generous baseline social preferences and appears to be present in males only. Our results highlight the relevance of baseline social preferences and sex in explaining the relationship between stress and prosociality.

Although altruistic behavior is well established, recent evidence suggests that it is only partly genuine, reflecting instead the desire to appear fair, either to themselves or to others.

In a lab experiment with 288 participants, we measured the extent of posturing and its relationship with other dimensions of social preferences. We implement a within-subject design that uses the different variations of the modified dictator game in Blanco et al. (2011) to elicit inequality concerns in Other-Other allocations and in Self-Other allocations in several cases: solely allocation (modified dictator game), under plausible deniability (moral wiggle room), and with the possibility to exert positive and negative reciprocity towards the allocator when in the role of the recipient. For the measurement of the moral wiggle room, our instrument allows not only to identify wrigglers, but also to convey an estimate of their posturing degree. In fact, departing from most of the tasks in the literature (based on the standard dictator game), our experimental protocol allows subjects to trade off their concern for money and reputational incentives at the margin without fully revealing their type.

More importantly, our design allows us to classify subjects along two dimensions: social image concern and deontological preferences. Once classified in this way, subjects show consistent, yet different, patterns of moral wiggle room and reciprocity. Overall, the use of the moral wiggle room is not prevalent. Only 38% of our subjects are less altruistic when their choice is hidden by the presence of a random draw than when it is fully observable. Interestingly those classified as Kantians (47% of our sample) are more prone to use the moral wiggle room than consequentialists (28%). While 37% of Kantians are moral wigglers, for consequentialists they represent only 29% of their group. Additionally, Kantians are more reciprocal in the intensive margin, but more likely to avoid punishing others. Moreover, non-reciprocal Kantians are often moral wrigglers.