10 Anchoring effect

Suppose you are the judge in a legal case of rape. The prosecutor and the defender have given their final speeches and you have just closed the court for a lunch break. The next session will start right after lunch, so that you have roughly an hour to make up your mind about the sentence. All the information that is necessary to make this important decision is right in front of you. The protocols of witnesses' statements, the opinions of a series of experts, and the relevant passages from the penal code are spread over your desk. You go through the most important facts once again: The victim's account of what happened that night, the expert's assessment of how likely it is that the defendant will commit rape again, the prosecutor's and the defender's plea. Upon close inspection, the evidence seems mixed and you are uncertain about what to do, what sentence to give. In thinking about the core facts, the final words of the prosecutor echo in your mind ". .. therefore , your honour, I demand a sentence of 34 months ". You wonder, " 34 months of prison confinement, is this an appropriate sentence? " Will the prosecutor's demand influence your sentencing decision? If so, your decision may be biased by one of the most remarkable influences on human judgement, namely the anchoring effect (Tversky & Kahneman, 1974). Because the prosecutor's goal is to obtain a high sentence , being directly influenced by his demand may be against your intentions. At the same time, it would put you in good company. The results of a recent study of ours (Englich & Mussweiler, 2001) indicate that accomplished trial judges with an average of more than 15 years of experience were influenced by sentencing demands, even if the demands were made by non-experts. In fact, the magnitude of this influence proved to be dramatic. Judges who considered a high demand of 34 months gave final sentences that were almost 8 months longer than judges who considered a low demand of 12 months. A difference of 8 months in prison for the identical crime. Notably, this influence occurred although both demands were explicitly made by a non-expert: In our study they were given by a computer science student in the role of the prosecutor.