The sweet jar

About this video

At the school fair there is a big jar of sweets, and whoever guesses closest wins the lot. Before Sara writes her guess, the boy next to her asks: more or less than 900, do you think? Sara writes 650. Later her brother Navid comes along, and the girl ahead of him asks: more or less than 90? Navid writes 200. The jar has the same sweets in it for both of them. Why are their guesses so far apart?

Both knew the number they heard was just a question, not a clue. Yet each guess ended up near it. Sara started from 900 and moved down, but not far enough; Navid started from 90 and moved up, but not far enough. The first number acted like an anchor, the weight that holds a boat in place so it can only drift a little way.

In 1974 the psychologists Amos Tversky and Daniel Kahneman showed how strong this pull is. They spun a wheel of numbers that was secretly set to stop on 10 or on 65, then asked how many of every 100 countries in the United Nations are in Africa. Everybody could see the wheel was pure luck. Still, people who saw 10 guessed about 25, and people who saw 65 guessed about 45. This pull is called anchoring, and it is used everywhere: a high old price next to the new one, or the first number said out loud in a deal.

Knowing about anchoring doesn't switch it off, but a few habits help. Make your own guess first and write it down. Ask where the number came from: is it a clue, or just the first thing someone said? And think of a reason it could be far off before you settle. This video goes with The First Number lesson of Knowledge Level 2 on Knaph.

Transcript

1. 0:00A jar of sweets. Whoever guesses closest wins them all.
2. 0:05Sara is asked, more than 900? She writes 650. Navid hears 90. He writes 200.
3. 0:11Each started from the number they heard and moved, but not far enough.
4. 0:17In 1974, a spun wheel moved people's guesses about Africa a long way.
5. 0:23Make your own guess first. Ask: is that number a clue?
6. 0:29Is it a clue, or just an anchor?