Addressing the "packaging" Problem in Stated Preference Studies
JONES P, University of Westminster, UK
Many stated preference studies in transport and other subject areas have found that the values obtained from SP for individual attributes of a package usually sum to more than the value of the package as a whole. In transport, this is primarily the case w
Many stated preference studies in transport and other subject areas have found that the values obtained from SP for individual attributes of a package usually sum to more than the value of the package as a whole. In transport, this is primarily the case when the package deals with 'secondary' factors such as station facilities or rolling stock.
There are a number of possible explanations for this effect. There may be some redundancy among the attributes, making the whole worth less than the sum of the parts (as is evidenced by the interaction terms found in some SP studies); there may be a 'capping' effect due to an overall budget constraint; or the values for each attribute may in part be capturing a trip consumer surplus, resulting in an element of'double' counting when the attribute values are summed.
The paper reviews findings from a number of transport studies to explore the size of the packaging effect and to see what can be learnt about the likely explanation. It also draws on a review of the wider marketing and economic literature, and results from group discussions among rail travellers.
It draws conclusions about the likely causes and consequences of the package effect, and goes on to question the appropriateness of the approach in relation to how travellers perceive and use such facilities.
It outlines an alternative approach to studying secondary factors, based on identifying the key function, which the facility performs and 'profiling' the level of provision against expectations*
Association for European Transport