Ökonomin erklärt warum sich Banker so schlecht verhalten haben

by Gastbeitrag on 21. Mai 2009

Anne Sibert ist Professorin und Leiterin der “School of Economics, Mathematics and Statistics at Birkbeck College” in London. In einem Beitrag für die angesehene Ökonomie-Website Voxeu hat sie drei Erklärungsansätze zum Verhalten der Banker zusammengefasst. Nach ihrer Ansicht gibt es drei Ursachen für das schlechte Verhalten von Bankmanagern:

  1. Kognitive Verzerrungen und Selbstüberschätzung auf Basis vergangener Erfahrungen
  2. Hohe Testosteronwerte der männlichen Banker, die zu höherer Risikoneigung führten (siehe dazu auch diesen Beitrag)
  3. Verzerrtes Bonussystem, das kurzfristigen Erfolg statt langfristige Ergebnisse honorierte

All die Punkte sind inhaltlich nicht neu, jedoch im Artikel von Sibert recht kompakt zusammengefasst, so dass ich diesen Beitrag, der außerdem ausgezeichnete Literaturangeben enthält, hier komplett unter den Lizenzbedingungen von VoxEu übernehme.

Why did the bankers behave so badly?

Anne Sibert, 18 May 2009

Greedy bankers are getting most of the blame for the current financial crisis. This column explains bankers did behave badly for mainly three reasons. They committed cognitive errors involving biases towards their own prior beliefs; too many male bankers high on testosterone took too much risk, and a flawed compensation structure rewarded perceived short-term competency rather than long-run results.

Many people share the blame for the current financial crisis; politicians, supervisors, regulators and even imprudent households and businesses. One group, however, has been judged to be especially guilty; the employees in the financial services sector. In response to their perceived greed and bad judgment, the US House of Representatives passed a bill that would effectively confiscate the 2008 bonuses of employees of financial firms receiving significant bailout assistance. In the UK, vandals smashed the windows and trashed the Mercedes of the former head of the Royal Bank of Scotland, while protestors tried to take over a London branch of the bank. In Iceland, financiers have wisely fled the country.

The populist outrage may be excessive, but it is hard to deny that certain aspects of these employees’ conduct were undesirable. Bankers imprudently counted on a continuation of the US housing boom long after most economists predicted its demise; they were overly sanguine about sustainable leverage ratios; managers of insurance companies and pension funds failed to exercise sufficient caution when they purchased collateralised debt obligations and asset-backed securities that they did not understand or know the value of. Since few would characterise the bankers and other employees of financial firms as an unintelligent group, it is interesting to ask why they behaved in such an egregious fashion; I advance three theories.

Humans are prone to cognitive errors

The first explanation is that humans are prone to cognitive errors involving biases towards their own prior beliefs. A vast empirical psychology literature documents that people fail to put sufficient weight on evidence that contradicts their initial hypotheses, that they are overconfident in their own ideas and have a tendency to avoid searching for evidence that would their disprove their own theories. Psychologists attribute these cognitive errors, collectively known as confirmation bias, to several factors. These include emotional reasons, such as embarrassment, stubbornness and hope, and cultural reasons, such as superstition and tradition. There may also be physiological explanations; the evolutionary development of the human brain may have facilitated the ability to use heuristics which provide good judgements rapidly, but which can also lead to systematic biases. In addition, recent research supports the theory that the human brain arrives at outcomes – such as confirming one’s own beliefs – that promote positive and minimise negative emotional responses.

Sexism and the City

UK Labour cabinet member Hazel Blears suggests a second reason, commenting that, “Maybe if we had some more women in the boardrooms, we [might] not have seen as much risk-taking behaviour” (Sullivan and Jordan 2009). Indeed, the financial services industry – one in which lap dancing is apparently considered appropriate corporate entertainment (UK Equality and Human Rights Commission) – is overwhelmingly male dominated. Women hold only 17% of the corporate directorships and 2.5% of the CEO positions in the finance and insurance industries in the US (Sullivan and Jordan 2009). In Iceland – home to a particularly spectacular collapse – it is said that there was just one senior woman banker, and that she quit in 2006 (Lewis 2009). If men are especially prone to being insufficiently risk averse and overly confident, then this male dominance may have contributed to the financial crisis.

There is a substantial economics literature on the effect of gender on attitudes toward risk and most of it appears to support the idea that men are less risk averse than women in their financial decision making.1 There is also a sizable literature documenting that men tend to be more overconfident than women. Barber and Odean (2001) find that men are substantially more overconfident than women in financial markets. In general, overconfidence is not found to be related to ability (see Lundeberg et al (1994)) and that success is more likely to increase overconfidence in men than in women (see, for example, Beyer (1990)). Thus, if confidence helps produce successful outcomes, there is more likely to be strong feedback loop in confidence in men than in women.

In a fascinating and innovative study, Coates and Herbert (2008) advance the notion that steroid feedback loops may help explain why male bankers behave irrationally when caught up in bubbles. These authors took samples of testosterone levels of 17 male traders on a typical London trading floor (which had 260 traders, only four of whom were female). They found that testosterone was significantly higher on days when traders made more than their daily one-month average profit and that higher levels of testosterone also led to greater profitability – presumably because of greater confidence and risk taking. The authors hypothesise that if raised testosterone were to persist for several weeks the elevated appetite for risk taking might have important behavioural consequences and that there might be cognitive implications as well; testosterone, they say, has receptors throughout the areas of the brain that neuro-economic research has identified as contributing to irrational financial decisions.

If – as the research may suggest – men are less risk averse than women, then a work group composed primarily of men (or primarily of women) may be a particularly bad idea. A vast psychology literature documents the phenomenon that group deliberation tends to result in an average opinion that is more extreme than the average original position of group members. If a group is composed of overly cautious individuals, it will be even more cautious than its average member; if it is composed of individuals who are overly tolerant of risk, it will be even less risk averse than its average member (Buchanan and Huczynski 1997).

Bonuses distort behaviour

In a recent paper, Hamid Sabourian and I advance a third reason for the behaviour of bankers; a flawed compensation structure that rewards perceived short-term competency, rather than good long-run results causes bankers to distort their behaviour in an attempt to increase their perceived ability (Sabourian and Sibert 2009). We suppose that a banker’s choices are unobservable. Bankers differ in their ability to make the correct decision and this ability is known only to themselves. In the long run, it can be determined whether the action chosen is the best one or not and the banker would rather make the correct decision than the wrong one. However, in the short run, the banker’s bonus depends upon how competent he is perceived to be.

In the first variant of our model, we suppose that a banker chooses an action and is then confronted with publicly observable conflicting information. He then chooses whether or not to change his course of action. If he is especially competent, then he knows that his original choice is probably still the best and does not change it. If he is less competent, the conflicting information tells him that his choice is probably not the best. We show that, for a range of banker competencies, even if the banker realises that his original choice is not likely to be the best, he does not change it. Instead, in the interest of receiving a higher bonus, he mimics an especially competent banker and continues with his original decision.

In the second variant of the model, the banker chooses an action. There is no publicly observed information in this case. Instead, the banker is asked how likely he thinks it is that his decision is the best. We think of this as a proxy for how strongly the banker sells his views to his employer or customers. In the long run, if the banker’s decision is wrong, he bears a cost that is increasing in his stated confidence. Even though it can be costly to claim to be correct with high probability and there is no intrinsic benefit from being overly optimistic, if bankers who are perceived to be especially competent receive high enough bonuses, then all bankers will imitate the most competent and oversell their decision.

In the third variant of the model, the banker chooses an action and is then given the opportunity to acquire additional information, at a cost, which, if his initial choice is incorrect, might confirm that it is incorrect. The banker could then abandon his original choice. Highly competent bankers are unlikely to devote resources to questioning their decision as they are unlikely to be wrong. Thus, less competent bankers attempt to increase their bonuses by masquerading as more competent ones; they do not search out additional information either.


1 See, for example, Jianakoplas and Bernasek (1998), Bernasek and Shwiff (2001), Holt and Laury (2002) and Eckel and Grossman (2002). Schubert et al (1999) is a rare exception. The differences between men and women may, of course, be due to nurturing rather than nature


Barber, Brad M. and Terrance Odean, “Boys will be Boys: Gender, Overconfidence and Common Stock Investment,” Quarterly Journal of Economics 66, 2001, 261-292.

Bernasek, Alexandra and Stephanie Shwiff, “Gender, Risk and Retirement,” Journal of Economic Issues 35, 2001, 345-356.

Beyer, Sylvia, “Gender Differences in the Accuracy of Self-Evaluations of Performance,” Journal of Personality and Social Psychology, 59, 1990, 960-970.

Buchanan, David and Andrzej Huczynski, Organizational Behaviour, London, Prentice-Hall, 1997.

Coates, J. M. and J. Herbert, “Endogenous Steroids and Financial Risk Taking on a London Trading Floor,” Proceedings of the National Academy of Sciences 105, 2008, 6167-6172.

Eckel, Catherine C. and Philip J. Grossman, “Sex Differences and Statistical Stereotyping in Attitudes toward Financial Risk,” Evolution and Human Behaviour 23, 2002, 281-295.

Holt, Charles A. and Susan K. Laury, “Risk Aversion and Incentive Effects,” American Economic Review 92, 2002, 1644-1655.

Jianakoplas, Nancy A. and Alexandra Bernasek, “Are Women more Risk Averse?Economic Inquiry 36, 1998, 620-630.

Lewis, Michael, “Wall Street on Tundra,” Vanity Fair, Apr. 2009.

Lundeberg, Mary A., Paul W. Fox and Judith Punccohar, “Highly Confident but Wrong: Gender Differences and Similarities in Confidence Judgements,” Journal of Educational Psychology 86, 1994, 114-121.

Sabourian, Hamid and Anne Sibert, “Banker Compensation and Confirmation Bias,” CEPR Working Paper no. 7263, Apr. 2008.

Schubert, Renate, Martin Brown, Matthias Gyster and Hans Wolfgang Brachinger, “Financial Decision Making: Are Women Really more Risk Averse?” American Economic Review 89, 1999, 381-385.

Sullivan, Kevin and Mary Jordan, “In Banking Crisis, Guys get the Blame: More Women Needed in Top Jobs, Critics Say,” Washington Post Foreign Service, 11 Feb. 2009.

Marcus Mai 22, 2009 um 11:03 Uhr

Man kann sich’s auch einfach machen – so wie Frau Sibert et al. mit dem Testosteron-Argument.

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