When knowledge matters-differential effects of available ... - CiteSeerX

European Journal of Social Psychology Eur. J. Soc. Psychol. 38, 896–904 (2008) Published online 26 November 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ejsp.479

When knowledge matters—differential effects of available knowledge in standard and basic anchoring tasks BIRTE ENGLICH* University of Cologne, Germany

Abstract The present research examines whether anchoring effects—the assimilation of a numeric estimate towards a previously considered standard—depend on judges’ available knowledge in the target domain. Based on previous research, I distinguish two types of anchoring effects. Standard anchoring is obtained if judges are explicitly asked to compare the anchor to the target. Basic anchoring results if the accessibility of the anchor is increased prior to judgments about the target. I expected that only basic but not standard anchoring is reduced by providing judges with judgment-relevant knowledge. Using a standard versus basic anchoring paradigm, 112 participants were confronted with a high versus low anchor before estimating the average price of a German midsize car. Prior to this task, participants were provided with information about prices of cars (relevant knowledge) versus kitchens (irrelevant knowledge). Results demonstrate that this knowledge only influenced the magnitude of basic but not standard anchoring effects. This finding demonstrates that knowledge has differential effects in different types of anchoring. Copyright # 2007 John Wiley & Sons, Ltd. When making numeric judgments, people are often influenced by irrelevant numbers. Estimates of the percentage of African nations in the UN depend on whether a high or a low number was previously determined by spinning a wheel of fortune (Tversky & Kahneman, 1974), sentencing decisions by criminal judges depend on whether a high or a low sentence was suggested by a journalist’s question (Englich, Mussweiler, & Strack, 2006), and estimates of the number of fellow students who will contract cancer depend on whether judges previously copied five pages of high numbers or five pages of words (Wilson, Houston, Etling, & Brekke, 1996). In fact, demonstrations of such anchoring effects are abundant (Chapman & Johnson, 2002; Epley, 2004; Mussweiler, Englich, & Strack, 2004). No matter whether judgments are made under the controlled conditions of the psychological laboratory (e.g. Chapman & Johnson, 1999; Epley & Gilovich, 2001; Mussweiler & Strack, 1999, 2000a; Strack & Mussweiler, 1997) or in real life settings (e.g. Chapman & Bornstein, 1996; Englich, 2005, 2006; Englich, Mussweiler, & Strack, 2005, 2006; Mussweiler, Strack, & Pfeiffer, 2000; Northcraft & Neale, 1987) are they reliably assimilated towards a salient anchor. Judges who anchor on a high number typically give higher estimates than those who anchor on a low number. This is even the case if an anchor is presented subliminally, outside of participants’ awareness (Mussweiler & Englich, 2005). Intuition suggests that one factor that is likely to influence such anchoring effects, is judges’ knowledge about the judgmental target. At first sight, it seems plausible to assume that the more knowledge judges have available, the less they are influenced by irrelevant anchors. An idealized judge who knows how many African, American, Asian and European nations are members of the UN, for example has little reason to rely on irrelevant anchors when asked to estimate the number of nations in the UN. All this judge has to do to arrive at this estimate is to sum up the existing knowledge about UN membership on the different continents. This seems an easy task to master and one that should not be drastically influenced by whether a high or low irrelevant anchor value is presented along side. Thus, it seems obvious that an inverse relationship between judges’ amount of knowledge about the judgmental target and the extent to which they are influenced by irrelevant anchor values should exist. *Correspondence to: Birte Englich, Institut fu¨r Allgemeine Psychologie und Sozialpsychologie, Humanwissenschaftliche Fakulta¨t, Universita¨t zu Ko¨ln, Gronewaldstrasse 2, 50931 Ko¨ln, Germany. E-mail: [email protected]

Copyright # 2007 John Wiley & Sons, Ltd.

Received 28 February 2007 Accepted 11 October 2007

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Surprisingly, the empirical evidence on how knowledge influences anchoring is less clear cut. On the one hand, it has been shown that sometimes knowledge does not reduce anchoring. In fact, research on the role of expertise in anchoring has repeatedly demonstrated that the magnitude of an obtained anchoring effect is independent of judges’ expertise. Recent research on anchoring effects in judicial decision-making provides particularly drastic demonstrations of this independence (for a recent review, see Englich, 2006). Here, it has been shown that experienced trial judges and legal laypeople show anchoring effects of similar magnitude (Englich & Mussweiler, 2001; Englich et al., 2005, 2006). Even if the anchor values are clearly irrelevant because they were randomly determined, experts and non-experts are influenced to similar extents. In particular, legal judges who specialized and had extensive experience in the particular domain of law to which a given legal case pertained (i.e. criminal law) were influenced by irrelevant and randomly determined anchors in much the same way as legal judges who specialized in a different domain of law (e.g. administrative law, civil law) and thus had no experience with similar cases (Englich et al., 2006). These findings demonstrate that more knowledgeable judges are not necessarily less influenced by a given anchor. In fact, it has been demonstrated that having more judgment-relevant knowledge accessible at the time the judgment is made, may even increase the amount of anchoring (Chapman & Johnson, 1999); inducing participants to activate knowledge about health-related behaviour, rendered their subsequent judgment about the ‘number of people who will die of heart disease or cancer in the next 10 years’ even more susceptible to anchoring influences. On the other hand, it has also been shown that sometimes knowledge reduces anchoring. For example Wilson et al. (1996) demonstrated that participants who rated themselves as more knowledgeable in the target domain were less influenced by the given anchors than participants who rated themselves as less knowledgeable. Based on these findings, it is thus difficult to answer the question: how does knowledge influence anchoring? Answering this question is further complicated by the fact that anchoring effects appear to be multifaceted—despite their unitary name which implies the existence of a unitary phenomenon. In fact, evidence is accumulating which suggests that different types of anchoring phenomena with quite different characteristics exist. With regard to anchoring effects that result from exposure to externally provided rather than internally generated anchors (see Epley & Gilovich, 2001), at least two distinguishable anchoring phenomena appear to exist: standard anchoring and basic anchoring (Wilson et al., 1996).

STANDARD AND BASIC ANCHORING EFFECTS Standard anchoring effects have been examined in a paradigm in which judges sequentially make a comparative and an absolute judgment about the critical target quantity. In the classic study introducing this standard anchoring paradigm (Tversky & Kahneman, 1974), judges were first asked to compare the percentage of African nations in the UN to the anchor value and indicate whether it is larger or smaller than this value. Subsequently, judges were asked to make their best estimate of the absolute percentage of African nations in the UN. These estimates were assimilated to the provided anchor values so that participants who had considered the high anchor gave higher estimates than those who had considered the low anchor. Basic anchoring effects have been demonstrated in paradigms that do not involve a direct comparison of anchor and target. Here, merely increasing the accessibility of the anchor value prior to the critical estimate is sufficient to produce anchoring effects (Wilson et al., 1996). In one of these studies, for example judges either copied five pages of high numbers or five pages of words before estimating the number of fellow students who would get cancer (Wilson et al., 1996, Study 3). Those who had copied five pages of high numbers gave higher estimates than those who had copied five pages of words. Although standard and basic anchoring are similar with respect to the effects they produce, they may be quite distinct with regard to the psychological mechanisms they involve (Mussweiler & Strack, 1999, 2001; Wilson et al., 1996). Specifically, standard anchoring effects appear to be produced by an elaborate hypothesis-testing mechanism in which judges selectively activate information indicating that the judgmental target is similar to the anchor value (Mussweiler & Strack, 1999, 2000a; Strack & Mussweiler, 1997; see also Chapman & Johnson, 1999). Here, the given anchor value is semantically tied to the judgmental target: knowledge that specifically implies that target and anchor are closely connected is generated. In marked contrast, basic anchoring effects do not involve such close ties between anchor and target. Rather, they appear to be produced by a fairly shallow numeric priming effect which focuses on the accessibility of the anchor value (Mussweiler & Strack, 2001; Wong & Kwong, 2000). Copying five pages of numbers increases their accessibility, so Copyright # 2007 John Wiley & Sons, Ltd.

Eur. J. Soc. Psychol. 38, 896–904 (2008) DOI: 10.1002/ejsp

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that judges who are looking for an appropriate standard of comparison when generating the critical estimate (Mussweiler, 2003) are likely to use one of them. In basic anchoring, a given anchor thus influences target judgments, because the anchor number just happens to be on the top of judges’ minds when they judge the target. In standard anchoring, however, a given anchor influences target judgments, because it has been semantically related and closely tied to the target in an elaborate hypothesis-testing mechanism (see Chapman & Johnson, 1999; Mussweiler & Strack, 1999; Strack & Mussweiler, 1997).

DIFFERENTIAL EFFECTS OF KNOWLEDGE ON STANDARD VERSUS BASIC ANCHORING This difference in their underlying psychological mechanisms implies that basic and standard anchoring may differentially depend on knowledge about the target domain. One aspect of differences in target knowledge is that the more judges know about a target, the more alternative anchors they have available. An idealized judge may, for example have accumulated a lot of knowledge about car prices, for example because he recently bought a new car. This judge may thus know the current prices for different car models and makes. When asked to estimate the average price of a midsize car, this judge thus has a large number of potential anchors he could use in the judgment process: the price of the car he just bought, or the prices of the other cars he did not buy. An idealized judge who has little knowledge about cars—for example because he only uses public transport—does not have such a plethora of anchors available. How will these two idealized judges be influenced by a given anchor value? I suggest that the extent to which the knowledgeable versus unknowledgeable judge are influenced by a given anchor, depends on how closely this anchor is tied to the target. If the anchor is presented in a standard anchoring paradigm, then judges generate substantial knowledge which exclusively ties the given anchor to the target, before they are asked to give an estimate of the target value. They test the hypothesis that the target value is equal to the given anchor, so that a specific anchor-consistent subset of target knowledge is easily accessible and will form the basis for the target judgment. In the standard anchoring paradigm, the fact that the knowledgeable judge might have alternative anchors available will not influence the target judgment, because these alternative anchors have not been related to the target. In contrast, if the anchor is presented in a basic anchoring paradigm, then judges have not linked the anchor value to the target before they generate the target estimate. The anchor is simply one accessible number that happens to be on the top of judges’ minds when they generate the estimate. To the extent that other potential anchors also happen to be on the top of judges’ minds, they may equally well be used during the judgment process. The knowledgeable judge in the basic anchoring paradigm who has more alternative anchors available is likely to use some of these alternative anchors during the judgment process. Doing so will reduce the influence of the given anchor. The unknowledgeable judge in the basic anchoring paradigm does not have any alternative anchors available, so that he exclusively uses the given anchor during the judgment process, which results in stronger anchoring influences. This reasoning suggests that available knowledge about the target domain will reduce the amount of basic anchoring but not standard anchoring.

THE PRESENT RESEARCH The present study tested this reasoning. To do so, judges were asked to estimate the average price of a German midsize car in a basic or a standard anchoring paradigm. In the basic anchoring paradigm, high versus low anchors were made accessible prior to the target judgment with the help of a handwriting task (Wilson et al., 1996). Participants were either asked to write down the numbers between 10 150 and 10 199 or those between 29 150 and 29 199. Previous research (Wilson et al., 1996) has demonstrated that doing so, influences subsequent numeric judgments, so that participants should assimilate their estimate about car prices to these anchors. In the standard anchoring paradigm, high versus low anchors were explicitly compared to the target prior to the target judgment. Participants were either asked to indicate whether the average price of a German midsize car is higher or lower than 10 175 or 29 175. Subsequent to these different types of anchor presentation, all participants estimated the average price of a German midsize car. Prior to these tasks, the amount of judgment-relevant knowledge that judges had available was manipulated. All participants received a booklet with five advertisements including the pictures, names and prices of consumer products. For half the participants, these products Copyright # 2007 John Wiley & Sons, Ltd.



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were cars so that they were directly exposed to relevant target knowledge prior to the anchoring task. For the other half, these products were kitchens with the exact same prices as the cars. These participants were thus exposed to judgment-irrelevant knowledge prior to the anchoring task. How would this exposure to judgment-relevant versus irrelevant knowledge influence the amount of anchoring that is obtained in the basic versus standard anchoring paradigm?

METHODS Participants We recruited 112 male university students as participants. They were contacted via phone, asked to participate in several unrelated studies and offered 6 Euro.

Materials and Procedures Upon arrival in the lab in groups of up to three, participants were greeted by the experimenter, led to an individual booth and handed a stack of folders which included the experimental materials. The experimenter informed participants that they were about to complete a series of tasks that were unrelated to one another and were only administered together for efficiency. To emphasize the unrelatedness of these studies, the materials were printed in different fonts. The first folder included the knowledge activation task. Instructions to this task informed participants that the ostensible goal was to find out which types of advertisements are particularly pleasant to watch. To examine this question, participants would be presented with a series of advertisements that presented products from different perspectives and would be asked to indicate how much they liked the design of each advertisement. Participants were presented with five different advertisements, each consisting of a 14.5 9.5 cm2 black and white photo that depicted a product, the name of the model and/or manufacturer, and the suggested retail price. Participants were asked to judge each of the advertisements with respect to three aspects: the extent to which they liked (1) the perspective from which the picture was taken, (2) the positioning of the price and (3) the design of the depicted product itself. Evaluations were given along seven-point rating scales ranging from 1 (not at all) to 7 (very much). For about half of the participants (relevant knowledge condition), the five ads depicted different models of German midsize cars, namely a Mercedes A-Class, an Opel Astra, a Ford Focus, a BMW 3-Series, a Volkswagen Golf. The presented prices for these cars were: 18 550, 15 600, 15 400, 24 000 and 14 700. For the other half of the participants (irrelevant knowledge condition) the five ads depicted kitchens from different manufacturers, namely Bulthaup, Schneider and Nolte. The prices were identical to those used in the car ads. Next, participants worked on the anchoring task. For about half of the participants (basic anchoring paradigm), the anchoring tasks were provided in two separate folders. For them, the second folder included a numeric anchor priming. Following the procedures of Wilson et al. (1996), these participants were informed that they were about to take part in a graphological study. Instructions pointed out that the goal of this research was to examine whether and how handwriting and character are related. As a first step, this required collecting samples of handwriting. Participants would be asked to write down 50 five-digit numbers. Specifically, participants in the low anchor condition were asked to write down the numbers between 10 150 and 10 199, participants in the high anchor condition were asked to write down the numbers between 29 150 and 29 199. After completion of this ‘graphological study’, participants proceeded with the third folder, which contained a ‘brief questionnaire which attempts to examine associations people have with cars’. On the first page of this questionnaire, participants were asked to take their time to think about the average price of a German midsize car. It was pointed out that at this point participants did not have to come up with a specific estimate. Rather, they should take about 1 minute to merely arrive at a broad idea of the average price and then to proceed with the next page. On the next page, participants were asked to provide a concrete estimate of the average price of a German midsize car. The estimation question read: ‘What do you think, how much does a German midsize car cost on average? ______’. For the other half of the participants (standard anchoring paradigm), the anchoring task was provided in one folder. Following the procedures of Strack and Mussweiler (1997), on a first page these participants were informed that they were about to take part in a pretest with the goal to find the best wording for general knowledge questionnaires. It was pointed Copyright # 2007 John Wiley & Sons, Ltd.


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out that some of the questions would contain numeric values and that these values had been determined by a randomization device. On the second page, participants were asked to provide two estimates about the average price of a midsize German car. Following the standard anchoring procedure (Tversky & Kahneman, 1974), participants were first asked to give a comparative judgment by indicating whether the average price of a German midsize car is higher or lower than the given anchor value. This value was equivalent to the mean of the numbers copied by participants in the numeric anchoring condition. Thus, participants were either confronted with a low anchor of 10 175 or with a high anchor of 29 975. Subsequent to this comparative judgment, participants were asked to provide their absolute judgment of the target value: ‘What do you think, how much does a German midsize car cost on average? ______’. After completion of these anchoring tasks, participants were debriefed using a funnelled debriefing rationale, thanked for their participation and paid. None of the participants were aware of the actual connection between the ostensibly unrelated studies. In sum, this study is based on a 2 (anchoring paradigm: standard vs. basic) 2 (knowledge activation: relevant vs. irrelevant) 2 (anchor: high vs. low) experimental design. All factors were manipulated between participants.

RESULTS I expected that whether the amount of anchoring is influenced by the type of knowledge that is activated, depends on which type of anchoring effect is examined. More specifically, I hypothesized that in standard anchoring, effects of similar magnitude are obtained no matter whether relevant or irrelevant knowledge is activated prior to the anchoring task. For basic anchoring, however, I hypothesized that activating relevant knowledge prior to the anchoring task would reduce the size of the anchoring effect. The means depicted in Figure 1 are consistent with these hypotheses. In the standard anchoring paradigm, a substantial anchoring effect was obtained no matter whether relevant or irrelevant knowledge was activated beforehand. Specifically,

Figure 1. Mean estimates for the average price of a German midsize car by anchoring paradigm (numeric vs. standard), knowledge activation (relevant vs. irrelevant) and anchor (high vs. low) Copyright # 2007 John Wiley & Sons, Ltd.



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participants who were exposed to irrelevant knowledge and were confronted with a high anchor gave higher estimates for the price of a German midsize car (M ¼ 20 600) than those who were confronted with a low anchor (M ¼ 16 125), t(104) ¼ 3.22, p < .002. The same was true for participants who were exposed to relevant knowledge (M ¼ 22 233 vs. M ¼ 14 923), t(104) ¼ 4.99, p < .001. In the basic anchoring paradigm, however, an anchoring effect was only obtained when no relevant knowledge had been previously activated. Specifically, participants who were exposed to irrelevant knowledge and were confronted with a high anchor, gave higher estimates for the price of a German midsize car (M ¼ 22 139) than those who were confronted with a low anchor (M ¼ 18 459), t(104) ¼ 2.51, p < .02. Participants who were exposed to relevant knowledge, however, gave similar estimates no matter whether they were confronted with high (M ¼ 18 885) or low anchors (M ¼ 19 227), t(104) ¼ .22, n.s. In a 2 (anchoring paradigm: standard vs. basic) 2 (information activation: relevant vs. irrelevant) 2 (anchor: high vs. low) ANOVA using participants’ estimates of the average price of German midsize cars as the dependent variable, this pattern produced a significant three-way interaction effect, F(1, 104) ¼ 5.44, p < .02, h2p ¼ .05. In this analysis, two additional significant effects emerged. The main effect anchor indicates that overall high anchors led to higher estimates than low anchors, F(1, 104) ¼ 26.48, p < .001, h2p ¼ .2. The anchoring paradigm \times anchor interaction indicates that overall stronger anchoring effects were obtained in the standard than in the basic anchoring paradigm, F(1, 104) ¼ 8.26, p < .01, h2p ¼ .07. Furthermore, there was a tendency for higher estimates to be given in the basic than in the standard anchoring paradigm, F(1, 104) ¼ 2.7, p < .1, h2p ¼ .03. None of the remaining effects approached significance, all Fs < 1.

DISCUSSION The present research examined how knowledge influences judgmental anchoring. Based on an analysis of the different psychological mechanisms that contribute to standard versus basic anchoring effects, I hypothesized that only the magnitude of basic anchoring effects is reduced if judges have judgment-relevant knowledge available, but not the magnitude of standard anchoring effects. The presented findings are consistent with this notion. They show that in standard anchoring, judges who were provided with judgment-relevant knowledge immediately before the anchoring task, were still influenced by the given anchor values. The size of the obtained anchoring effect was not reduced by providing judgment-relevant knowledge. A mere inspection of the means even reveals that if anything, judges who had relevant knowledge available tended to be more strongly influenced by the anchor values than those who did not. This tendency is consistent with the results of Chapman and Johnson (1999), who found that increasing the accessibility of judgment-relevant knowledge prior to a standard anchoring task led to greater anchoring than increasing the accessibility of judgment-irrelevant knowledge. In basic anchoring, however, only judges who were provided with judgment-irrelevant knowledge were influenced by the given anchors. Judges who had relevant knowledge available remained uninfluenced. Knowledge thus has differential effects on basic and standard anchoring effects. At first sight, this finding appears to be inconsistent with the findings of Wilson et al. (1996) who demonstrated that for standard and basic anchoring alike, knowledgeable judges are less influenced by the anchors than unknowledgeable ones. This inconsistency, however, is more apparent than real because knowledgeability is operationalized in strikingly different ways in both studies. Whereas I directly manipulated the amount of judgment-relevant knowledge participants had available immediately before the anchoring task, Wilson et al. (1996) assessed how knowledgeable participants judged themselves after giving their estimate. In this study, participants were asked to indicate ‘how knowledgeable they were about the number of countries in the United Nations’ (p. 390) after having estimated this quantity. It seems likely that this judgment depends on how confident one is about the judgment. The possibility that judged knowledgeability and confidence are related is suggested by the fact that both appear to be influenced by the magnitude of anchoring in similar ways. In fact, Jacowitz and Kahneman (1995) demonstrated that participants who were less influenced by anchoring subsequently judged themselves to be more confident. These ambiguities emphasize the importance of directly manipulating the amount of knowledge judges have available. At the same time, it is important to note that in the present study, I necessarily had to focus on one particular manipulation of knowledge. Specifically, participants were or were not exposed to a range of prices for the critical target category. Clearly, alternative operationalizations of knowledge are conceivable. One could, for example provide Copyright # 2007 John Wiley & Sons, Ltd.


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participants with more elaborate background knowledge about the target category, or recruit participants with a lot versus a little knowledge in the target domain. The present conceptualisation holds that these alternative manipulations of knowledge would lead to similar effects. This needs to be substantiated by future research. The present findings extend the existing anchoring literature in a number of important ways. Foremost, they take a closer look at the role of knowledge in judgmental anchoring. In doing so, the present research provides further evidence for the striking robustness of standard anchoring effects. Previous research has demonstrated that standard anchoring effects are robust against a variety of manipulations that are geared towards discrediting the anchor and inducing judges to correct for its potential influence. The present findings supplement this body of evidence on standard anchoring by showing that even if judges are provided with judgment-relevant knowledge that allows them to determine a good estimate, are they influenced by irrelevant anchor values. All participants, who were provided with car prices prior to the anchoring task, needed to do was to calculate the mean of these prices or simply report the price of the most prototypical German midsize car. Although more informative alternative anchors were thus available so that more accurate estimates seem easy to determine, judges’ estimates are influenced by irrelevant anchors. This finding extends an earlier conceptualisation of the role of knowledge in standard anchoring. Mussweiler and Strack (2000a, 2000b) have suggested that judges’ knowledge may be represented by a distribution of subjective probabilities for possible values of the target (Wyer, 1973). A participant’s estimate corresponds to the subjective expected value of this distribution which can vary with respect to its position along the judgemental dimension and its dispersion. Different positions along the judgmental dimension reflect different expected values and thus different estimates. Different dispersions reflect different levels of knowledgeability. The more judges know about the target, the narrower the dispersion of possible values. Mussweiler and Strack (2000a, 2000b) further propose that how an anchor is processed depends on whether it falls within or outside of the distribution of possible values. If an anchor falls within this distribution (i.e. it is plausible), it is processed by testing the hypothesis that the target quantity is equal to the anchor. If an anchor falls outside of this distribution (i.e. it is implausible), it is initially processed by quickly consulting category knowledge to determine a plausible boundary value, which is then used for hypothesis testing. This conceptualisation thus focuses on how judges’ knowledge influences anchor processing via differences in perceived anchor plausibility. As a consequence, in their research Mussweiler and Strack (2000a, 2000b) focus on extreme differences in knowledge—differences that are sufficiently large to render the same anchor value plausible versus implausible. They demonstrate that for such extreme differences, more knowledgeable judges are less influenced by the given anchors. Participants who do at least know the target category of a fictitious target named Xiang Long, for example are less influenced than participants with no knowledge at all (Mussweiler & Strack, 2000b). Presumably, this is the case, because for the latter group, any anchor is plausible and thus induces participants to test the possibility that the target quantity is equal to the anchor. Unlike this work, the present research focuses on how less extreme differences in available target knowledge influence the magnitude of standard anchoring effects. Rather than examining fictitious targets for which, by definition, judges have no pre-existing judgment-relevant knowledge, I used a target for which all participants have at least some background knowledge. Furthermore, the anchor values were deliberately selected to be plausible. Given that differential processing of plausible versus implausible anchors forms the heart of Mussweiler and Strack’s (2000b) view of knowledge effects in standard anchoring, their perspective is difficult to apply to the present study. The present findings supplement the research by Mussweiler and Strack (2000b) by demonstrating that for differences in knowledge that are too small to lead to differential perceptions of anchor plausibility, the magnitude of anchoring is independent of judges’ available target knowledge. In this respect and under these conditions, knowledge does not matter for standard anchoring. The present findings not only demonstrate the robustness of standard anchoring. At the same time, they demonstrate the fragility of basic anchoring effects. It has been suggested (Brewer & Chapman, 2002) that in marked contrast to standard anchoring, basic anchoring is a much weaker effect that is tied to the specific manipulations used in the original demonstration (Wilson et al., 1996). The present finding is one of the few (see Brewer & Chapman, 2002) that replicates the basic anchoring effect and establishes one of its boundary conditions. Basic anchoring is only obtained if judges have little judgment-relevant knowledge available. If relevant knowledge is available no anchoring occurs. Therefore, knowledge does matter for basic anchoring. This differential effect of knowledge on basic versus standard anchoring effects highlights the fact that both are distinct phenomena. Basic anchoring effects appear to be produced by a fairly shallow numeric priming mechanism (Wong & Kwong, 2000) whereas standard anchoring appears to be produced by a more elaborate hypothesis-testing mechanism in which judges selectively search for and activate target knowledge that closely ties the anchor to the target (Mussweiler & Copyright # 2007 John Wiley & Sons, Ltd.



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Strack, 1999). The present study suggests that this difference in underlying mechanisms may entail a difference in how strongly both types of effects are influenced by the amount of judgment-relevant knowledge judges have available. Standard anchoring effects appear to be more robust than basic anchoring effects, in that they are less dependent on how much judgment-relevant knowledge judges have available. In addition, the described difference in underlying mechanisms is likely to produce further differences in the robustness of both effects. It has been demonstrated (Mussweiler & Strack, 1999) that standard anchoring effects are so strikingly robust, because they are produced by the knowledge that participants have generated themselves. Because such self-generated knowledge is less likely to be seen as a biasing source of judgment (Johnson, Hashtroudi, & Lindsay, 1993; Mussweiler & Neumann, 2000), judges are unlikely to be aware of anchoring influences in the standard paradigm. Basic anchoring effects, on the other hand, do not appear to be produced by such self-generated knowledge. As a consequence, judges are more likely to be aware of this potentially biasing source. Given that awareness of the influence is a first precondition for judgmental correction (Wilson & Brekke, 1994), this reasoning suggests that basic anchoring effects may be easier to correct for than standard anchoring effects. In this respect, the current findings emphasize the fact that despite its unitary label, anchoring is a multifaceted phenomenon (Epley, 2004; Mussweiler & Strack, 2001; Wilson et al., 1996). Anchoring effects differ with respect to the psychological mechanisms they involve and the characteristics of the consequences they produce.

ACKNOWLEDGEMENTS This research was supported by the German Research Foundation (DFG). I would like to thank Irene Futterlieb, Simone Dohle and Thomas Dunlap for their indispensable practical support.

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