Anchoring and Adjustment

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).