It is widely known that financial markets can become dangerously unstable, yet it is unclear why. Recent research has highlighted the possibility that endogenous hormones, in particular testosterone and cortisol, may critically influence traders’ financial decision making. Here we show that cortisol, a hormone that modulates the response to physical or psychological stress, predicts instability in financial markets. Specifically, we recorded salivary levels of cortisol and testosterone in people participating in an experimental asset market (N = 142) and found that individual and aggregate levels of endogenous cortisol predict subsequent risk-taking and price instability. We then administered either cortisol (single oral dose of 100 mg hydrocortisone, N = 34) or testosterone (three doses of 10 g transdermal 1% testosterone gel over 48 hours, N = 41) to young males before they played an asset trading game. We found that both cortisol and testosterone shifted investment towards riskier assets. Cortisol appears to affect risk preferences directly, whereas testosterone operates by inducing increased optimism about future price changes. Our results suggest that changes in both cortisol and testosterone could play a destabilizing role in financial markets through increased risk taking behaviour, acting via different behavioural pathways.

We study how cognitive abilities correlate with behavioral choices by collecting evidence from almost 1, 200 subjects across eight experimental projects concerning a wide variety of tasks, including some classic risk and social preference elicitation protocols. The Cognitive Reflection Test (CRT) has been administered to all our experimental subjects, which makes our dataset one of the largest in the literature. We partition our subject pool into three groups depending on their CRT performance. Reflective subjects are those answering at least two of the three CRT questions correctly. Impulsive subjects are those who are unable to suppress the instinctive impulse to follow the intuitive -although incorrect-answer in at least two 2 questions. The remaining subjects form a residual group. We find that females score significantly less than males in the CRT and that, in their wrong answers, impulsive ones are observed more frequently. The 2D-4D ratio, which is higher for females, is correlated negatively with subjects' CRT score. We also find that differences in risk attitudes across CRT groups crucially depend on the elicitation task. Finally, impulsive subjects have higher social (inequity-averse) concerns, while reflective subjects are more likely to satisfy basic consistency requirements in lottery choices. JEL Classification: C91, D81, J16

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The COVID-19 pandemic forced almost all professional football matches worlwide to be played in empty stadiums. This large-scale natural experiment offers a unique opportunity to assess the impact of social pressure on decision making and behavior. In particular, I investigate the effect of the home crowd on match outcomes and referee decisions. Using a large dataset from 41 professional football leagues in 30 different countries, I find that the home advantage in match outcomes drops by around one half and that referee bias against away teams completely disappears following the lockdowns. My results therefore suggest that social pressure exerted by home crowds has an important effect on the behavior of referees and on game outcomes.

Correlative evidence suggests that testosterone promotes dominance and aggression. However, causal evidence is scarce and offers mixed results. To investigate this relationship, we administered testosterone for 48h to 41 healthy young adult men in a within-subjects, double-blind placebo-controlled balanced crossover design. Subjects played the role of responders in an ultimatum game, where rejecting a low offer is costly, but serves to destroy the proposer's profit. Such action can hence be interpreted as non-physical aggression in response to social provocation. In addition, subjects completed a self-assessed mood questionnaire. As expected, self-reported aggressiveness was a key predictor of ultimatum game rejections. However, while testosterone affected subjective ratings of feeling energetic and interested, our evidence strongly suggests that testosterone had no effect on ultimatum game rejections or on aggressive mood. Our findings illustrate the importance of using causal interventions to assess correlative evidence.