Assessing the influence of design dimensions on stated choice experiment estimates

This paper explores the complexity and cognitive burden associated to stated choice experiments. Complexity 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 attribute 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 complexity 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 willingness-to-pay estimates.