In designing our protocol, we assumed that traders would experience a large endocrine reaction only if the risks they were taking and the consequent profit and loss were large enough to matter to them; if, that is, the trading would meaningfully affect their income, reputation, or, in the worst case, chances of being fired. We therefore decided to conduct the study on a real trading floor rather than under laboratory conditions and to sample steroids while traders did their normal jobs (9). With permission from the managers of a midsized trading floor (≈260 traders, of which 4 were female) in the City of London, we recruited 17 male traders to participate in the study.