A good Stated Preference survey helps respondents to make real trade-offs between attributes of the alternatives presented, and to state their real preferences. In terms of all valuation methods this means that the possibilities for giving protest and strategic answers is minimised. And in terms of Stated Choice (SC) this means that attribute levels must be well balanced and that the choice situation must not be too complex. As a result the proportion lexicographic choices will be reduced. This paper presents a survey among public transport users in Oslo, where 6 different questionnaire designs were used. Three different methods were used and combined: Stated Choice (SC), Transfer Price (TP) and 'Frisch Method' (FM), named after the 1969 Nobel Price laureate Ragnar Frisch, who launched a new and simple way to circle in respondents' trade-offs between attributes in a sequence of questions. Overlapping tests have been run in order to check respondents for consistency across the methods. Relatively good correspondence was found between individual respondents' preferences and valuations across the methods. For example, respondents who sort their answers lexicographically according to one attribute in SC have also a tendency towards higher willingness to pay (WTP) for the same attribute in TP. However, while the valuations of travel time factors are relatively stable, the proportions of zero-valuations and lexicography vary to a great degree between the methods. The major problem of zero-valuations in TP is reduced significantly with the new FM approach. In many respects, therefore, FM is regarded as a superior method to TP. In order to make the SC design more flexible the variation of the price level has been adjusted according to WTP obtained in the preceding TP questions. Although not significant, there is a clear trend towards lower proportions lexicographic answers in SC with this method to fine-tune the appropriate price level variations. Combined use of valuation methods is therefore found to (i) improve the flexibility of the SC design; (ii) to determine the degree to which respondents answer consistently; and (iii) to compare the performance of each method. For the covering abstract see ITRD E124693.
Samenvatting