Številke so premalo, ljudje potrebujemo zgodbo

Odličen komentar Davida Leonhardta o iluziji človeške racionalnosti. Slednja predvideva, da ljudje razmišljamo v sistemu kompleksnih povezav in se odločamo na podlagi ocenjenih verjetnosti posameznih dogodkov. Če nam nekdo številčno predstavi verjetnosti nastopa nekih dogodkov, nam to olajša, da v kompleksnem svetu sprejmemo pravilne odločitve na podlagi zaporedja dogodkov, določenega z verjetnostjo njihovega nastopa.

Toda to je wishul thinking, kot je ugotovil že nobelovec Daniel Kahneman, ko je svetoval izraelski obveščevalni službi. Ljudje smo bistveno manj racionalni in si poskušamo poenostaviti naše odločitve. Če ima nek dogodek nizko verjetnost, slednjo zaokrožimo navzdol na nič. Torej, da se dogodek sploh ne bo zgodil. Če ima dogodek 50% verjetnost, slednjo zaokrožimo nazvgor – na popolno verjetnost, da se bo zgodil. Oboje pa je lahko skrajno zavajujoče in tudi boleče napačno, saj nizka verjetnost ne pomeni, da se redek dogodek ne bo tudi zgodil ali obratno.

Ljudje zato potrebujemo zgodbe, potrebujemo kontekst, da lahko verjetnostim posameznih dogodkov damo ustrezno težo v našem predstavnostnem svetu. Potrebujemo sliko povezav. Zato je tako povedna stara modrost, da slika pove več kot tisoč besed. In zato tudi jaz od študentov zahtevam, da si pri empiričnih nalogah vedno najprej narišejo povezave v graf. Eno je operirati z abstraktnimi korelacijskimi koeficienti, povsem nekaj drugega pa je videti distribucije pojavov in vse neregularnosti (nagnjenost, osamelce itd.) v grafičnem prikazu.

The Israeli intelligence service asked the great psychologist Daniel Kahneman for help in the 1970s, and Kahneman came back with a suggestion: Get rid of the classic intelligence report. It allows leaders to justify any conclusion they want, Kahneman said. In its place, he suggested giving the leaders estimated probabilities of events.

The intelligence service did so, and an early report concluded that one scenario would increase the chance of full-scale war with Syria by 10 percent. Seeing the number, a top official was relieved. “Ten percent increase?” he said. “That is a small difference.”

Kahneman was horrified (as Michael Lewis recounts in his book “The Undoing Project”). A 10 percent increase in the chance of catastrophic war was serious. Yet the official decided that 10 wasn’t so different from zero.

Looking back years later, Kahneman said: “No one ever made a decision because of a number. They need a story.”

But I now think explanation is doomed to fail. For an individual event, people can’t resist saying that a probability was “right” if it was above 50 percent and “wrong” if it was below 50 percent. When this happens, those of us who believe in probabilities can’t just shake our heads and mutter about white Christmases. We have to communicate more effectively.

I think part of the answer lies with Kahneman’s insight: Human beings need a story.

It’s not enough to say an event has a 10 percent probability. People need a story that forces them to visualize the unlikely event — so they don’t round 10 to zero.

Welch, a Dartmouth professor, pointed me to an online pictograph about breast-cancer risk. It shows 1,000 stick figures, of which 973 are gray (no cancer), 22 are yellow (future survivor) and five are red (die in next 10 years). You can see the most likely outcome without ignoring the others.

Vir: Davida Leonhardt, New York Times

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