Heuristics and Biases

Anchoring effect

Making use of a reference point or anchor to come up with an estimate

Kahneman and Tversky

A: how anchors influence thinking and decision making

P: spun a wheel with numbers from 1 to 100/wheel was fixed so would always land on 10 or 60/participants were asked to estimate what percentage of U.N. member countries were African countries

F: participants who spun 10 gave a lower estimate than participants who spun 60/mean estimate for ‘low anchor group’ was 25% compared 45% for ‘high anchor group’

C: random number had an anchoring effect on participants estimates

Evaluate Kahneman and Tversky

• Well controlled experiment: demonstrated a clear casual relationship between high or low number spun on the wheel and estimate for African membership in the U.N.

• Simple experiment: reliable

• All American university students: low generalisability

Availability Heuristic

People judge the likelihood of an event based on how easily an example or instance of the event comes to mind

Kahneman and Tversky

A: how the availability heuristic affects judgement

P: asked ‘if a random word is taken from the English language, is it more likely that the word starts with the letter K or that K is the third letter?’

F: 105 out of 152 participants thought it was more likely that words in English would begin with the letter K/there are twice as many words in English that have K as the third letter than there are words that begin with K

C: much easier to think of words that begin with the letter K (kitchen) than words that have K as the third letter (ask)/because it is easier to recall words that begin with K, participants incorrectly assume that there are more words like this

Evaluate Kahneman and Tversky

• Simple: high reliability

• Low ecological validity: artificial task

• All American college students: low generalisability