Person-specific Models in SP Analysis
P Sola Conde and M Wardman, ITS, University of Leeds, UK;
Given that Stated Preference surveys based on choice experiments typically collect multiple responses from each individual contacted in the survey, it is natural to ask whether it is useful to develop choice models for each respondent. Person-specific models are often used in general marketing studies. Thesemodels could be used in the transport context either as final products to understand and predict behaviour or as an intermediate stage in the development of more sophisticated models of population behaviour.
Study of person-specific models has been inhibited by the results of work by Morikawa (ref. about 1990), who found that person-specific models performed much less well than models based on poolingthe data from all respondents. However, recent work by Kroes and Cirillo (1999) suggests that Morikawa?s findings may apply to a smaller range of circumstances than had been thought, thus opening the possibility that person-specific models could be useful in some circumstances.
The paper reports the results of a study undertaken at ITS Leeds in which simulated data is used to investigate the circumstances in which person-specific models could be useful. By varying the assumptions underlying simulated behaviour, it was possible to represent a range of circumstances and to investigate the success of person-specific models in each case. Some areas for further research are identified. An important step in the investigation is the specification of appropriate ways to measure the success of models in reproducing the simulation assumptions and two separate measures have been defined and applied.
The results indicate that in most circumstances person-specific models are not as successful as models based on pooled data, but when inter-personal variation is high, in ways that are described in the paper,person-specific models might indeed be useful. Thus in extreme cases it may be useful to investigate person-specific models as an intermediate step to developing a population model, but in most cases Morikawa?s conclusions remain valid.
The paper will be of value to SP researchers in developing methodology by indicating the limits of applicability of simple analysis methods and how to proceed when those limits are passed. The new aspects of this work are that it goes beyond the previous studies in terms of the realism of the error structures considered, therefore giving better insight into the true extent of applicability of person-specific modelling.
Association for European Transport