De-biasing Anchoring and Adjustment: The Use of Multiple

Anchors

Bridgett MilnerEd Hirt

MPA PresentationThanks to:

Amy Johnson, Kelly Koch, Erin Steury, and Kristin Hendrix

Anchoring and Adjustment!(a brief review)

• The anchoring and adjustment heuristic involves the significant influence of an arbitrary reference point (an anchor) on estimates and judgments (Tversky and Kahneman, 1974).

o Is Mt. Everest taller or shorter than 10 miles? How tall is Mt. Everest?

• 5.5 miles

More on Anchoring and Adjustment!

• Anchoring and adjustment allows for judgments to be made under uncertainty conditions, through allowing the individual (most often) a reasonable starting point from which to adjust (Tversky and Kahneman, 1974).

• The influence of this anchor is such that judgments are insufficiently adjusted away from this reference point (the anchor) toward the true value.

Bias

• The use of this strategy, or heuristic, typically causes a bias in estimates reflected in this insufficient adjustment, such that judgment is biased toward the initial values presented (the anchor). Bias becomes more extreme as anchor points become more extreme relative to the true value.

Standard Anchoring Procedure• Most often demonstrated through the standard

anchoring paradigm in which participants are given an anchor to which they make two responses. These responses are:1. a “comparative” judgment

• asked to compare the anchor to their estimate or target response (most often asked to judge whether the actual, true value is above or below the supplied anchor)

2. an “absolute” judgment • asked to give their best estimate of the target response

(or the “true” value).

Example of Standard Anchoring Paradigm

• Is the percentage of African Nations in the UN greater or less than ____? (e.g.,65% or 10%)– Respond

• What is the number of African Nations in the UN?– Respond (mean estimate of high anchor =

45%, mean estimate of low anchor= 25%)

Robust• Regardless of type of anchoring task used,

findings are quite robust. Anchoring occurs in many paradigms and with many types of estimates including those on issues individuals care deeply about such as nuclear war estimates.

• Anchoring occurs even when the anchor provided is irrelevant to the study question (such as an assigned participant number or a completely unrelated statistic) or so extreme as to be completely implausible as a response.

Really Robust

• Anchoring has been demonstrated in information rich real world settings and with experts in the anchoring estimation task (Northcraft and Neale, 1987).

Avoiding the Bias—Background for this Study

• Use of the anchoring and adjustment heuristic in decision making seems fairly unavoidable.– laboratory experiments find that participants are often

completely unaware that an anchor influenced their response (Tversky and Kahneman, 1974; Northcraft and Neale, 1987, many others).

– when told about anchoring and adjustment and warned to avoid the use of this heuristic, effects remain (Plous, 1993).

– attempts at accuracy such as monetary incentives for correct judgments have no effect (Wilson, Houston, Eitling, & Brekke, 1996).

– To date, within traditional anchoring studies, the only time in which bias was not found was when participants had not paid attention to the supplied anchor (Wilson et al, 1996)…well sort of (we’ll get to that)

Mechanism: SAM – More Background for this Study

• Mussweiler and Strack’s Selective Accessibility Model is used to account for anchoring findings.– When given an anchor, initially set value as equal to

anchor. Test this using a positive test strategy which selectively scans ones memory for supporting evidence. This scan causes confirming evidence to become more available. This available information is used to make estimate.

– More robust than semantic priming due to self-generated nature of prime.

A new attempt to de-bias (at least in part): This study!

• Perhaps can de-bias anchoring and adjustment in the same way one de-biases the explanation bias in social judgment---through the “consider the opposite technique” (Lord, Lepper, & Preston, 1984; Mussweiler, Strack, & Pfeiffer, 2000) or “consider any plausible alternative” (Hirt & Markman, 1995). – De-biases through priming stimuli other than the

ones previously assessed (Hirt & Markman, 1995)---participants use ‘simulation heuristic’ to engage in “multiple simulation runs of potential outcomes”.

Consider the Opposite(or the Red Sox not winning against the Yankees)

• Within social judgment (and anchoring) considering the opposite outcome (or anchor) de-biases social judgments. – When first asked to think about “why might the

Red Sox win against the Yankees” –judgments become biased and people think “yeah, the Red Sox are going to win.”

– If asked to then think about “why the Red Sox might not win against the Yankees”--judgments now become unbiased.

Consider an Alternative(or Carrie winning American Idol)

• Interestingly, work by Hirt & Markman (1995) finds that you needn’t just consider the opposite to produce de-biasing effects though. They found that considering any alternative outcome (even when that outcome was in the same direction as the original one) produced de-biasing.– So in their paper, when participants explained a team winning

by both a close-margin and a landslide, de-biasing occurred! Also when explain 2 teams winning de-biasing occurs!

– So think about Bo winning American Idol---explanation bias leads to individuals thinking this is more likely---now think about Carrie winning---de-biased.

This study’s hypotheses

1. Traditional anchoring effects will occur in standard traditional anchoring questions.

2. When participants “consider the opposite,” de-biasing will occur.

3. When participants “consider an alternative,” de-biasing will occur

Procedure• 2 conditions (1 control; 1 experimental)

– Control condition asked trivia questions (given no anchor)

– Experimental condition –standard anchoring paradigm--(5 different questionnaires all with same 15 trivia questions---each participant responds to:

• 3 high anchor questions • 3 low anchor questions• 3 2-high anchor questions• 3 2-low anchor questions• 3 1-high 1-low anchor questions

Additional Measures

• Prior to completing the anchoring questions participants completed a short questionnaire asking about individual difference information.

• Participants responded to– demographic information (age, gender, and race)– A self-report of “trivia-knowledge” on a 1-7 scale– The NFC scale

Questions!

1. When did the Titanic sink? 1912 Mean Cntrl=1910 anch: 1850, 1867, 1947, 1954

2. How long is a blue whale at birth (in feet)? 25 19.45 2, 4, 44, 60

3. How many hours does it take for a snake to digest a frog (on average)?

50 21.2 1, 2, 34, 42

4. How many eggs does the average American consume each year?

286 236.4 24, 30, 400, 500

5. In what year was the planet Neptune discovered?1846 1829.6 1601, 1756, 1972, 1974

Etc….

Results!!

• Overall, differences between the 5 experimental conditions were found F(4,800)=390.44, p<.001.

• Post hoc t-tests follow on the upcoming slides as do t-tests comparing experimental conditions with control responses.

Traditional Anchoring Effects

Traditional anchoring effects were found– T-test comparing (z-scores of) high anchoring

conditions and control conditions• t (293)= -6.380, p<.001

– High anchor mean = .6002– Control mean = -.0889

– Low conditional and control• t (297) = 5.878, p<.001

– Low anchor mean = -.5853– Control mean = -.0889

Consider the Opposite

Considering the Opposite was seemingly an effective de-biasing technique.– Control versus High and Low anchor given btw Ss t-test

• t (299) = -.834, p=.405– Control mean = -.0889– High and Low anchor mean = .0046

– High and Low anchor given leads to significantly less high estimates than high anchor condition and significantly higher estimates than low anchor condition.

• t (217) = 11.725, p<.001 (high vs both w/in Ss t-test)• t (221) = -12.043, p<.001 (low vs both w/in Ss t-test)

– High mean = .5287– Both mean = .0008– Low mean = -.5551

Consider an Alternative

• Considering 2 anchors in the same direction did not de-bias overall but instead led to even more severe biasing than single anchors .

• t (216) = -4.011, p<.001 (high vs 2-high w/in Ss t-test)

• t (221) = 2.449, p<.05 (low vs 2-low w/in Ss t-test)– High mean = .5276– 2-High mean = .6687– Low mean = -.5556 – 2-Low mean = -.6472

More on Consider an Alternative• Recent follow up research by Hirt, Kardes, &

Markman (2004) finds that this consider an alternative de-biasing strategy is moderated by the individual difference “need for structure” such that:– individuals low in need for structure are more

affected by this de-biasing technique than those who are high.

• Within their research they find in fact that for low need for structure individuals, the alternative considered needn’t even be in the same domain for effective de-biasing to occur.

Need for Structure• Need for structure is characterized by the desire to

maintain with some extent of permanence a specific solution that has been seized upon.

• This personality characteristic is measured by facets 1, 2, and 4 of the Need for Closure scale (which can be broken into 5 different facets [3 being decisiveness and 5 being closed-mindedness]) (Neuberg, Judice, & West, 1997).

• Past research has found that this individual difference (NFS) leads to stronger anchoring effects (Kruglanski).

Need for Structure Results• Significant differences between high and low

NFS participants were found across the 4 experimental conditions in which bias was found (low, 2 low, high, & 2 high anchors). This difference was always that individuals low in NFS were significantly less biased than individuals high in NFS.

• Low: F(1, 257)=6.41, p<.05 high=-.61 low=-.48

• High: F(1,253)=6.85, p<.01 high= .63 low=.48

• 2 Low: F(1, 254)=109.23, p<.001 high=-.78 low=-.41

• 2 High: F(1, 254)=109.23, p,.001 high= .94 low=.36

More on NFS• For the high and low anchor conditions

(consider the opposite), all participants were de-biased, showing no differences from the control condition.

• For conditions in which 2 anchors were presented in the same direction (consider an alternative) :– For low NFS participants, de-biasing effects were

found such that when 2 anchors were presented participants showed less bias than in the traditional single anchor conditions• Low: t(114)=1.17, p=.09 1=-.48 2=-.41• High: t(111)=2.83, p<.01 1= .49 2= .36

Continued…

– For high NFS participants, presenting 2 anchors in a single direction worked in the opposite direction such that, rather than de-biasing estimates, estimates became more biased.

• Low: t(131)=3.18, p<.01 1=-.61 2=-.78• High: t(135)=4.64, p<.001 1= .63 2= .94

Discussion---Hypotheses revisited1. Traditional anchoring effects will occur in

standard traditional anchoring questions.

2. When participants “consider the opposite,” de-biasing will occur.

3. When participants “consider an alternative,” de-biasing will occur.

Discussion---Hypotheses revisited Traditional anchoring effects will

occur in standard traditional anchoring questions. Single high anchor led to significantly

higher estimates than control and single low anchor led to significantly lower estimates than control.

2. When participants “consider the opposite,” de-biasing will occur.

3. When participants “consider an alternative,” de-biasing will occur.

Discussion---Hypotheses revisited Traditional anchoring effects will occur in standard traditional anchoring

questions.

When participants “consider the opposite,” de-biasing will occur.

Consider the opposite condition estimates did not significantly differ from control estimates.

3. When participants “consider an alternative,” de-biasing will occur

Discussion---Hypotheses revisited Traditional anchoring effects will occur in standard traditional anchoring questions. When participants “consider the opposite,” de-biasing will occur.

When participants “consider an alternative,” de-biasing will occur.

Consider an alternative ONLY worked as a de-biasing strategy for participants low in need for structure. For individuals high in need for structure, considering two anchors in the same direction actually led to more extreme anchoring effects.

Individuals high in NFS (consistent with Kruglanksi’s findings) made significantly more biased estimates in the direction of the anchor (or anchors) than individuals low in need for structure

Summary

• De-biasing of anchoring (like the explanation bias) using a consider an alternative strategy is moderated by the individual difference NFS.– For individuals low in NFS, considering an

alternative is effective as a de-biasing technique.– For individuals high in NFS, de-biasing is much

more difficult. For these individuals considering an alternative does not work. To de-bias individuals high in NFS one must really be extreme in their de-biasing strategy and provide an opposite anchor rather than any other anchor.