We use ghost matches induced by Covid19 in the Bundesliga, Germany's top two football (soccer) divisions, to investigate whether audiences affect referees. We find that relative to the pre-Covid19 period, the difference between home and away teams in fouls and the number of cards increases. The results provide evidence for a home bias in referee decisions through social pressure.

We use ghost matches induced by Covid19 in the Bundesliga, Germany's top two football (soccer) divisions, to investigate whether audiences affect referees. We find that pre-Covid19 referees gave fewer fouls and yellow cards for the home team relative to the away team. These differences in fouls and cards changed during the ghost matches so that home teams were treated less favorably than before. This effect is concentrated in matches where support for the away team is particularly weak. The results provide evidence for a home bias in referee decisions through social pressure.

The enforcement of social norms is the fabric of a functioning society. Through the lens of two experiments, we examine how motives for lying and norm perceptions steer enforcement. Our contribution is to investigate the extent to which norm breaches are sanctioned, how normnudges affect the observed punishment behavior, and how the enforcement is linked to norm perceptions. Using a representative U.S. sample, Experiment 1 provides robust evidence that norm-enforcement is not only sensitive to the extent of the observed transgression (= size of the lie) but also to its consequences (= whether the lie remedies or creates payoff inequalities). We also find norm enforcers to be sensitive to different norm-nudges that convey social information about actual lying behavior or its social disapproval. To explain the punishment patterns, Experiment 2 examines how norms are perceived across different transgressions and how normnudges change these perceptions. We observe a malleability of social norm perceptions: norm nudges are most effective when pre-existing norms are vague. Importantly, we also find that punishment patterns in the first experiment closely follow these norm perceptions. Our findings suggest that norm enforcement can be successfully nudged and thus represent an expedient alternative to standard incentive-based interventions.

This paper studies the impact of the presence of human subjects in the role of a seller on bidding in experimental second-price auctions. Overbidding is a robust finding in secondprice auctions, and spite among bidders has been advanced as an explanation. If spite extends to the seller, then the absence of human sellers who receive the auction revenue may bias upwards the bidding behavior in existing experimental auctions. We derive the equilibrium bidding function in a model where bidders have preferences regarding both, the payoffs of other bidders and the seller's revenue. Overbidding is optimal when buyers are spiteful only towards other buyers. However, optimal bids are lower and potentially even truthful when spite extends to the seller. We experimentally test the model predictions by exogenously varying the presence of human subjects in the roles of the seller and competing bidders. We do not detect a systematic effect of the presence of a human seller on overbidding. We conclude that overbidding is not an artefact of the standard experimental implementation of second-price auctions in which human sellers are absent.

We show that a one-off incentive to bias advice has persistent effects. In an experiment, advisers were paid a bonus to recommend a lottery which only risk-seeking individuals should choose to a less informed client. Afterwards, they had to choose for themselves and make a second recommendation to another client, without any bonus. These advisers choose the risky lottery and recommend it a second time up to six times more often than advisers in a control group who were never offered a bonus. These results are consistent with a theory we present which is based on advisers' image concerns of appearing incorruptible.