On visible choice sets and scope sensitivity

In this paper we argue that the burgeoning empirical debate over scope sensitivity within contingent valuation studies is fundamentally incomplete in that it has neglected a systematic examination of certain effects of study design upon observed scope sensitivity. In particular we highlight the fact that in certain study designs the choice set initially offered (or "visible") to respondents is changed in a stepwise manner as they progress through a valuation exercise, while other designs involve advance disclosure regarding the full extent of the final visible choice set prior to any choices or values being elicited. The issue of changes in the visible choice set is alluded to by Smith (J. Environ. Econom. Manage. 22(1) 71), who identifies this as a primary challenge to Kahneman and Knetsch's (J. Environ. Econom. Manage. 22(1) 57), well-known experimental results. Kahneman and Knetsch contend that it seems "highly implausible that this minor procedural change would significantly alter results" (p. 61), but do not test this assertion. We present experimental and field tests of the impact upon contingent values of varying the visible choice set through stepwise and advance disclosure. These dimensions of design are interacted with changes in the order in which nested goods are presented (bottom-up versus top-down). When a stepwise disclosure procedure is adopted, the observed scope sensitivity is substantially and significantly affected by the order in which goods are presented but such procedural variance is not observed within advance disclosure designs. Conjectures regarding the origin and implications of such findings are presented. (C) 2003 Elsevier Science (USA). All rights reserved.