Assessing the influence of design dimensions on stated choice experiment estimates Sebastia ´n Caussade a , Juan de Dios Ortu ´zar a, * , Luis I. Rizzi a , David A. Hensher b a Department of Transport Engineering, Pontificia Universidad Cato ´lica de Chile Casilla 306, Co ´digo 105, Santiago 22, Chile b Institute of Transport Studies, Faculty of Economics and Business, The University of Sydney, NSW 2006, Australia Received 4 December 2003; received in revised form 22 July 2004; accepted 27 July 2004 Abstract This paper explores the complexity and cognitive burden associated to stated choice experiments. Com- plexity is analysed in terms of design dimensions such as the number of available alternatives, the number of attributes used to define these alternatives, the number of levels for those attributes, the range of attri- bute levels and the number of choice situations presented to each respondent. These design dimensions were systematically varied according to an experimental design in a first design hierarchy; the second hierarchy comprised the attributes of each alternative (travel times and travel cost components). To study the com- plexity of the experiment we specified a heteroskedastic logit model with the scale parameter specified as a function of the design dimensions. This allowed us to separate the effects of choice complexity from the marginal utility estimates. Our results show that all five design dimensions affect the choice variance, or put it another way, they affect choice consistency. However, we did not find systematic effects on willing- ness-to-pay estimates. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Stated choice design; Design of designs; Choice complexity; Heteroskedastic logit 0191-2615/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.trb.2004.07.006 * Corresponding author. Tel.: +56 2 686 4822; fax: +56 2 553 0281. E-mail address: jos@ing.puc.cl (J. de D. Ortu ´zar). www.elsevier.com/locate/trb Transportation Research Part B 39 (2005) 621–640