Tennis, testosterone and the winner effect

The Australian Open crowd hushes as the second set begins. The centre-court match at Rod Laver Arena is all it was promised: the players are ranked nearly identically by the WTP; both showed comparably good form in the run up to the Open; and the first set tie-break was decided by the narrowest possible margin - just two points. It’s anyone’s game! Or is it?


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Actually, statistical analysis of hundreds of thousands of professional tennis matches (when narrowed to the parameters above) reveals the winner of the first set is 60 per cent more likely to go on to win - when it’s a men’s match.

"Whether we are elite athletes or market traders we cannot escape the waves of hormones that course through our bodies."
Matt Nicol, BlueNotes contributing editor

Intriguingly, when it is a women’s match, the outcome is far less predictable.

Tennis has provided arguably the cleanest example of what is called ‘the winner effect’ – a phenomenon well established among animals but also present among humans.


In the wild, the winner effect is seen when two animals square off in a fight and the psychology is well understood.

Ahead of the skirmish, both contestants experience a rise in testosterone levels (regardless of sex); this perfectly legal self-doping scheme primes the body for competition. Reaction speeds quicken, blood carries oxygen faster and the brain experiences a notable increase in fearlessness – and risk appetite. 

The effect sees winners emerge with a tenfold increase in the amount of testosterone, while losers’ levels suppressed by the inverse amount. It’s how nature primes winners to push on (and keep winning) and for losers to withdraw (and recover).  

It is worth noting women produce on average about 90 per cent less testosterone than men. And, accordingly, the statistics for the outcome of close games (as outlined above) don’t show any correlation for the women players. The disparity is discussed in more detail in Wired.


The pioneering study and analysis of the winner effect was conducted by John Coates, former Wall Street trader and author of the book The Hour Between Dog and Wolf in which he explores phenomena he observed during the 90s.

I first heard Coates talk about his innovative use of tennis data to support his neuroscience hypothesis when he was presenting to a group of City traders in London (and scored a signed copy of his book!)

He describes working through the dotcom boom: “It was like watching A Midsummer Night’s Dream. Traders were euphoric and investors delusional. I would see people get on a winning streak on the trading floor and go lunatic. It happened to me as well…You think you’re infallible.”

Coates has also explored how high levels of another hormone, cortisol, can affect trader behaviour.

In an experiment conducted at Addenbrooke’s Hospital in Cambridge, tablets were used to raise subjects’ cortisol levels by about 55 per cent.

“It absolutely nuked their appetite for risk,” Coates told Wired. “In economics there’s an unstated assumption that our risk preferences are innate. This suggests the opposite. Our risk preferences fluctuate with the state of the body.”


When it comes to financial markets, Coates says men are more hormonal than women.

In fact, several studies have shown in some aspects, female investment managers outperform their male counterparts.

"It's not that one group is better than the other," he told Wired. "They're different. It's just that by diversifying the biology of the trading floor you would counterbalance the extreme tendencies."

The role of testosterone is an area of great interest for sports psychology too. More than driving muscle growth testosterone drives behavioural change.


Coates’ work is a compelling reminder we are not beings of pure human intellect; whether we are elite athletes or market traders we cannot escape the waves of testosterone, cortisol and other hormones coursing through our bodies.

As humans, our species shares much of our biology with other animals. We carry with us traits nature developed which allow us to make the most of each opportunity to win. And, through winning, the fitness to survive and evolve.

Matt Nicol is a contributing editor at BlueNotes

The views and opinions expressed in this communication are those of the author and may not necessarily state or reflect those of ANZ.

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