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Negotiations are complex, ill-structured, and uncertainty-prone processes subject to half-truths, tricks, and other means of psychological warfare (Ströbel, 2003, Ch. 2). In other words, negotiating is a demanding task with plenty of potential for making mistakes. As Bazerman (2006) points out, identifying and understanding systematic mistakes may lead to improved negotiation processes as well as facilitate the engineering of negotiation support systems. One possible systematic bias in negotiations regards attachment and the endogeneity of reference points and preferences. The following historical example illustrates the importance of endogenous reference points in negotiations, i.e. reference points that emerge in a negotiation as a results of the negotiation itself.

Since negotiators are decision-makers, understanding a negotiation requires a deep understanding of the negotiators’ decisions. As Hayek suggests, the theoretical foundations in this chapter address decision-making and preferences from the viewpoint of different disciplines. The origin of preferences and their stability over time varies widely across fields: Economists, for example, usually assume preferences to be an underlying property of any individual and to be stable over time. If an agent’s choice changes over time, then either the production technology available or the information at hand have changed—preferences do not. This widely used perspective is most notably vindicated by Stigler and Becker (1977) in a seminal paper arguing against the assumption of changing preferences and it is outlined in several microeconomic textbooks, e.g. Kreps (1990), Varian (1992), Mas-Colell, Whinston, and Green (1995).

As Bazerman points out, in a negotiation two or more parties are interested in reaching one of several possible agreements, but their preferences over these agreements are not completely identical. In multi-issue negotiations, studied here, parties usually have the possibility to simultaneously negotiate over several issues and to search for integrative potential. Negotiators play a non-constant-sum game.

Whether the attachment effect is present and reference-dependent preferences change systematically in multi-issue negotiations is empirically tested in two closely related experiments. In this chapter, an internet experiment that tests the existence of an attachment effect in negotiation is outlined. The results support the assumption that the preferences of negotiators are systematically affected by the offers exchanged. However—as with any experiment—the external validity of results might be questioned: an single experiment can never proof that the same results would emerge if any of the numerous design choices would be altered. To increase validity, a second experiment was conducted; it is reported in Chapter 5. The design of this second experiment is refined by lessons learned from the first experiment and purposefully differs in several respects to show that the attachment effect is not closely related to the design choices made.

The internet experiment reported in the Chapter 4 supports the existence of an attachment effect in negotiation: Negotiators form issue-wise reference points during a negotiation and these reference points influence their preferences. To strengthen this result, a laboratory experiment is conducted. The major differences in the design of the two experiments are incentive compatibility, bundles of durable consumer goods instead of attributes of a hypothetical rent contract, a larger sample size, and several distinct measures for treatment effects (cf. Sec. 4.3).

The study of offers, expectations, reference points, and attachment in negotiations classifies as ‘science of negotiation’. It is concerned with understanding the cognition and behavior of negotiators and contributes to the descriptive foundations of negotiation analysis from which advice how to negotiate rationally can be deduced. Personal characteristics that belong to the ‘art of negotiation’, on the other hand, were not considered in the present work.