Suppose I spin a Wheel of Fortune device as you watch, and it comes up pointing to 65. Then I ask: Do you think the percentage of countries in the United Nations that are in Africa is above or below this number? What do you think is the percentage of UN countries that are in Africa? Take a moment to consider these two questions yourself, if you like, and please don’t Google.
Also, try to guess, within five seconds, the value of the following arithmetical expression. Five seconds. Ready? Set . . . Go!
1 × 2 × 3 × 4 × 5 × 6 × 7 × 8
Tversky and Kahneman recorded the estimates of subjects who saw the Wheel of Fortune showing various numbers.1 The median estimate of subjects who saw the wheel show 65 was 45%; the median estimate of subjects who saw 10 was 25%.
The current theory for this and similar experiments is that subjects take the initial, uninformative number as their starting point or anchor; and then they adjust upward or downward from their starting estimate until they reach an answer that “sounds plausible”; and then they stop adjusting. This typically results in under-adjustment from the anchor—more distant numbers could also be “plausible,” but one stops at the first satisfying-sounding answer.
Similarly, students shown “1 × 2 × 3 × 4 × 5 × 6 × 7 × 8” made a median estimate of 512, while students shown “8 × 7 × 6 × 5 × 4 × 3 × 2 × 1” made a median estimate of 2,250. The motivating hypothesis was that students would try to multiply (or guess-combine) the first few factors of the product, then adjust upward. In both cases the adjustments were insufficient, relative to the true value of 40,320; but the first set of guesses were much more insufficient because they started from a lower anchor.
Tversky and Kahneman report that offering payoffs for accuracy did not reduce the anchoring effect.
Strack and Mussweiler asked for the year Einstein first visited the United States.2 Completely implausible anchors, such as 1215 or 1992, produced anchoring effects just as large as more plausible anchors such as 1905 or 1939.
There are obvious applications in, say, salary negotiations, or buying a car. I won’t suggest that you exploit it, but watch out for exploiters.
And watch yourself thinking, and try to notice when you are adjusting a figure in search of an estimate.
Debiasing manipulations for anchoring have generally proved not very effective. I would suggest these two: First, if the initial guess sounds implausible, try to throw it away entirely and come up with a new estimate, rather than sliding from the anchor. But this in itself may not be sufficient—subjects instructed to avoid anchoring still seem to do so.3 So, second, even if you are trying the first method, try also to think of an anchor in the opposite direction—an anchor that is clearly too small or too large, instead of too large or too small—and dwell on it briefly.
1Amos Tversky and Daniel Kahneman, “Judgment Under Uncertainty: Heuristics and Biases,” Science 185, no. 4157 (1974): 1124–1131.
2Fritz Strack and Thomas Mussweiler, “Explaining the Enigmatic Anchoring Effect: Mechanisms of Selective Accessibility,” Journal of Personality and Social Psychology 73, no. 3 (1997): 437–446.
3George A. Quattrone et al., “Explorations in Anchoring: The Effects of Prior Range, Anchor Extremity, and Suggestive Hints” (Unpublished manuscript, Stanford University, 1981).
You're a few years behind on this research, Eliezer.
The point of the research program of Mussweiler and Strack is that anchoring effects can occur without any adjustment. "Selective Accessibility" is their alternative, adjustment-free process that can produce estimates that are too close to the anchor. The idea is that, when people are testing the anchor value, they bring to mind information that is consistent with the correct answer being close to the anchor value, since that information is especially relevant for answering the comparative question. Then when they are then asked for their own estimate, they rely on that biased set of information that is already accessible in their mind, which produces estimates that are biased towards the anchor.
In 2001, Epley and Gilovich published their first of several papers designed to show that, while the Selective Accessibility process occurs and creates adjustment-free anchoring effects, there are also cases where people do adjust from an anchor value, just as Kahneman & Tversky claimed. The examples that they've used in their research are trivia questions like "What is the boiling point of water on Mount Everest?" where subjects will quickly think of a relevant, but wrong, number on their own, and they'll adjust from there based on their knowledge of why the number is wrong. In this case, most subjects know that 212F is the boiling point of water at sea level, but water boils at lower temperatures at altitude, so they adjust downward. This anchoring & adjustment process also creates estimates that are biased towards the anchor, since people tend to stop adjusting too soon, once they've reached a plausible-seeming value.
Gilovich and Epley have shown that subjects give estimates farther from the anchor (meaning that they are adjusting more) on these types of questions when they are given incentives for accuracy, warned about the biasing effect of anchors, high in Need For Cognition (the dispositional tendency to think things through a lot), or shaking their head (which makes them less willing to stop at a plausible-seeming value; head-nodding produces even less adjustment than baseline). None of these variables matter on the two-part questions with an experimenter provided anchor, like the Africa UN %, where selective accessibility seems to be the process creating anchoring effects. The relevance of these variables is the main evidence for their claim that adjustment occurs with one type of anchoring procedure but not the other.
The one manipulation that has shown some promise at debiasing Selective Accessibility based anchoring effects is a version of the "consider the opposite" advice that Eliezer gives. Mussweiler, Strack & Pfeiffer (2000) argued that this strategy helps make a more representative set of information accessible in subjects' minds, and they did find debiasing when they gave subjects targeted, question-specific instructions on what else to consider. But they did not try teaching subjects the general "consider the opposite" strategy and seeing if they could successfully apply it to the particular case on their own.
Mussweiler and Gilovich both have all of their relevant papers available for free on their websites.
Epley, N., & Gilovich, T. (2001). Putting adjustment back in the anchoring and adjustment heuristic: Differential processing of self-generated and experimenter-provided anchors. Psychological Science, 12, 391–396.
Mussweiler, T., Strack, F., & Pfeiffer, T. (2000). Overcoming the inevitable anchoring effect: Considering the opposite compensates for selective accessibility. Personality and Social Psychology Bulletin, 26, 1142-1150.
There have actually been several studies I've seen indicating that body-language is a feedback loop rather than just a communication output. Forcing yourself to smile will actually make you slightly happier, etc.