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“It’s tough to make predictions, especially about the future”*…




As astrophysicist Mario Livo recounts in Brilliant Blunders, in April 1900, the eminent physicist Lord Kelvin proclaimed that our understanding of the cosmos was complete except for two “clouds”—minor details still to be worked out. Those clouds had to do with radiation emissions and with the speed of light… and they pointed the way to two major revolutions in physics: quantum mechanics and the theory of relativity.  Prediction is hard; ironically, it’s especially hard for experts attempting foresight in their own fields…

The idea for the most important study ever conducted of expert predictions was sparked in 1984, at a meeting of a National Research Council committee on American-Soviet relations. The psychologist and political scientist Philip E. Tetlock was 30 years old, by far the most junior committee member. He listened intently as other members discussed Soviet intentions and American policies. Renowned experts delivered authoritative predictions, and Tetlock was struck by how many perfectly contradicted one another and were impervious to counterarguments.

Tetlock decided to put expert political and economic predictions to the test. With the Cold War in full swing, he collected forecasts from 284 highly educated experts who averaged more than 12 years of experience in their specialties. To ensure that the predictions were concrete, experts had to give specific probabilities of future events. Tetlock had to collect enough predictions that he could separate lucky and unlucky streaks from true skill. The project lasted 20 years, and comprised 82,361 probability estimates about the future.

The result: The experts were, by and large, horrific forecasters. Their areas of specialty, years of experience, and (for some) access to classified information made no difference. They were bad at short-term forecasting and bad at long-term forecasting. They were bad at forecasting in every domain. When experts declared that future events were impossible or nearly impossible, 15 percent of them occurred nonetheless. When they declared events to be a sure thing, more than one-quarter of them failed to transpire. As the Danish proverb warns, “It is difficult to make predictions, especially about the future.”…

One subgroup of scholars, however, did manage to see more of what was coming… they were not vested in a single discipline. They took from each argument and integrated apparently contradictory worldviews…

The integrators outperformed their colleagues in pretty much every way, but especially trounced them on long-term predictions. Eventually, Tetlock bestowed nicknames (borrowed from the philosopher Isaiah Berlin) on the experts he’d observed: The highly specialized hedgehogs knew “one big thing,” while the integrator foxes knew “many little things.”…

Credentialed authorities are comically bad at predicting the future. But reliable– at least more reliable– forecasting is possible: “The Peculiar Blindness of Experts.”

See Tetlock discuss his findings at a Long Now Seminar.  Read Berlin’s riff on Archilochus, “The Hedgehog and the Fox,” here.

* Yogi Berra


As we ponder prediction, we might send complicating birthday greetings to Edward Norton Lorenz; he was born on this date in 1917.  A mathematician who turned to meteorology during World War II, he established the theoretical basis of weather and climate predictability, as well as the basis for computer-aided atmospheric physics and meteorology.

But he is probably better remembered as the founder of modern chaos theory, a branch of mathematics focusing on the behavior of dynamical systems that are highly sensitive to initial conditions… and thus practically impossible to predict in detail with certainty.

In 1961, Lorenz was using a simple digital computer, a Royal McBee LGP-30, to simulate weather patterns by modeling 12 variables, representing things like temperature and wind speed. He wanted to see a sequence of data again, and to save time he started the simulation in the middle of its course. He did this by entering a printout of the data that corresponded to conditions in the middle of the original simulation. To his surprise, the weather that the machine began to predict was completely different from the previous calculation. The culprit: a rounded decimal number on the computer printout. The computer worked with 6-digit precision, but the printout rounded variables off to a 3-digit number, so a value like 0.506127 printed as 0.506. This difference is tiny, and the consensus at the time would have been that it should have no practical effect. However, Lorenz discovered that small changes in initial conditions produced large changes in long-term outcome. His work on the topic culminated in the publication of his 1963 paper “Deterministic Nonperiodic Flow” in Journal of the Atmospheric Sciences, and with it, the foundation of chaos theory…

His description of the butterfly effect, the idea that small changes can have large consequences, followed in 1969.

lorenz source


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