The tallest tree

About this video

Is the tallest tree in the world taller or shorter than 400 metres? Write down your guess. Did the number 400 change it? Most people say no. They knew 400 was only part of a question. The tallest tree known is a redwood in California, about 116 metres tall, and people asked with a high number guess far higher than people asked with a low one.

Knowing a subject well doesn't protect you. In 1987 Gregory Northcraft and Margaret Neale had estate agents in Arizona value the same house with the same pack of facts. Only the asking price changed. Agents who saw about 120,000 dollars said it was worth about 114,000; agents who saw about 150,000 said about 129,000. Asked what they had based their value on, few even mentioned the asking price.

Birte Englich, Thomas Mussweiler and Fritz Strack (2006) went further: experienced judges in Germany read a made-up shoplifting case and rolled a pair of dice, secretly loaded to total 3 or 9, before deciding the sentence. After a 9 they gave about 8 months, after a 3 about 5.

Why? The mind starts at the anchor and moves away from it, step by step, until the answer starts to feel possible, and then it stops. That first possible answer is on the edge nearest the anchor, so the guess stops too soon. This is called adjusting from an anchor. An expert does the same, only from a better start, and since the pull comes with no feeling, nobody notices it. What helps: make your own number before you see anyone else's, and ask why the anchor could be far off, both too high and too low.

Transcript

1. 0:00Is the tallest tree taller or shorter than 400 metres? Did that number change your guess?
2. 0:07Estate agents valued the same house. A higher asking price made it worth fifteen thousand dollars more. Few noticed.
3. 0:16Judges rolled loaded dice. After a nine, they gave longer sentences than after a three.
4. 0:23The mind starts at the anchor and moves away, but stops as soon as the answer feels possible.
5. 0:32Make your own number first. Then ask why the anchor could be far off.
6. 0:39Knowing a lot doesn't switch it off.