Rats, mazes, and the power of self-fulfilling prophecies

27th August, 2020

It’s 1963. A young psychologist named Bob Rosenthal conducts an experiment in which his assistants place rats in mazes, and then time how long it takes the rats to find the exit. They are housed in two cages: one for the smartest rats and one for rodent mediocrities. The assistants are not surprised to find that the smart rats solve the mazes more quickly.

Their supervisor is — because he knows that in truth, both cages contain ordinary lab rats. Prof Rosenthal — he would go on to chair Harvard’s psychology department — eventually concluded that the secret ingredient was the expectations of his assistants: they treated the “special” rats with care and handled the “stupid” rats with disdain. When we expect the best, we get the best — even if we expect it of a rat.

The story is well told in Rutger Bregman’s new book Humankind. His interest in Prof Rosenthal’s work is not hard to explain. Mr Bregman argues that people are fundamentally friendly and self-motivated. But he also argues that when we expect more of each other then, like the rats, we rise to the occasion. If schools, police or corporations believe that people are sluggish, dishonest or lazy, they may be proved right.

Prof Rosenthal coined the phrase “the Pygmalion effect”, the name inspired by Ovid’s account of a sculptor whose infatuation with a statue brings it to life. But the Pygmalion effect is just one example of what the sociologist Robert K. Merton called “self-fulfilling prophecies”.

There’s the placebo effect and its malign twin, the “nocebo effect”: if the doctor tells you a drug may produce side effects, some patients feel those side effects even if given an inert pill.

Self-fulfilling prophecies are a staple of economics. A recession can be caused by the expectation of a recession, if people hesitate to spend, hire or invest. And a bank run is the quintessential self-fulfilling prophecy.

The self-defeating prophecy is just as fascinating, and a problem that bedevils economic forecasters. If I credibly predict a surge in the price of oil next year, the surge will happen immediately as oil traders buy low now to sell high later. The forecast goes awry precisely because people thought it was accurate.

The coronavirus era has brought us a vivid example. A vocal minority argues that Covid-19 is not much worse than the influenza we ignore every winter, so both mandatory lockdowns and voluntary precautions have been unnecessary.

A glance at the data gives that argument a veneer of plausibility. The UK has suffered about 65,000 excess deaths during the first wave of the pandemic, and 25,000-30,000 excess deaths are attributed to flu in England alone during bad flu seasons. Is the disparity so great that the country needed to grind to a halt?

The flaw in the argument is clear: Covid was “only” twice as bad as a bad flu season because we took extreme measures to contain it. The effectiveness of the lockdown is being used as an argument that the lockdown was unnecessary. It is frustrating, but that is the nature of a self-defeating prophecy in a politicised environment.

One might say the same thing about Fort Knox. Nobody has ever tried to steal the gold, so why bother with all the guards?

Self-fulfilling prophecies can be pernicious; writing in 1948, Prof Merton focused on racism. For example, some said African Americans were strikebreakers who thus should not be allowed to join trade unions. Prof Merton pointed out that their exclusion from unions was the reason they had been strikebreakers. Sexism also drips with self-fulfilling prophecies. Since our leaders were usually straight white men in the past, it is all too easy to favour such people for leadership roles in the future.

Such prophecies can also be harnessed for good. Bob Rosenthal took his ideas into schools, where he found that what is true of rats being respectfully handled is just as true of pupils. Persuade a teacher that a pupil has hidden talents and the child will soon flourish.

Yet one can put too much faith in the self-fulfilling prophecy. Fervent excitement about the dizzy ascent of Tesla’s share price should help the company sell cars and raise funds but, in the long run, the value of a Tesla share will be determined by Tesla’s profitability.

Self-fulfilling prophecies are particularly tempting for politicians. It is all too easy to paint a project such as Brexit in Tinker Bell terms: if we clap our hands and believe in Brexit, it will not disappoint. Conveniently, all setbacks can be blamed on “Remoaners”.

The fact is that some things are false no matter how fervently we wish them to be true. We often plunge into projects with rosy views of how long they will take and how successful they will be, but our optimism only gets us started. It does not finish the job.

I think we should try to treat each other with kindness and respect, and not just because it worked for Bob Rosenthal’s rats. But there are limits to the power of sheer positive thinking. Even in the cartoons, Wile E. Coyote eventually feels the tug of gravity.

Written for and first published in the Financial Times on 17 July 2020. My NEW book The Next Fifty Things That Made the Modern Economy is NOW OUT. Details, and to order on Hive, Blackwells, Amazon or Watersones. Bill Bryson comments, “Endlessly insightful and full of surprises — exactly what you would expect from Tim Harford.”

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