The Measurement and Evaluation of Diversity of Opportunity
N Ferguson, University of Strathclyde, UK
This paper introduces the concept of diversity of opportunity and demonstrates links with and the potential to extend commonly used measures of accessibility.
The diversity of opportunity afforded by a city has been identified as a vital ingredient to the quality of urban living, particularly once satisficing levels of opportunity have been achieved. As such it may be considered to be an important dimension of sustainability. At the level of the individual decision-maker, diversity may be valued in a number of ways which are relevant to transport, land use and accessibility. These include freedom of choice, well-being and circumstances in which an individual wishes to retain flexibility over future actions. For example, the choice over residential location can be construed as an occasion where value is derived inter alia from a desire to seek variety or to insure against particular eventualities.
At the neighbourhood level, the promotion of diversity in terms of both land-use and social mix is regarded as a key policy objective which supports, amongst other things, sustainable travel patterns. Several ad hoc measures of diversity have been proposed in the literature and these have found application in studies of location choice and travel-related behaviour. However, these measures offer only a limited interpretation of the concept of diversity and take no account of the preferences of individuals.
Diversity has emerged as an important concept in a number of other fields including ecology, marketing, culture, economics, philosophy and social welfare. Several notable and comprehensive reviews now exist which examine theoretical and methodological issues and consider the potential for developing a unified approach to the treatment of diversity. There exist several points of intersection between this literature and measures of accessibility commonly used in transport-related studies. Drawing on this work, this paper seeks to extend current interpretations of accessibility to encompass diversity of opportunity, to develop practical methods of measuring diversity and to illustrate the application of these methods with an empirical example.
In the first part of this paper, criteria and methods for ranking sets of objects are considered. It is shown that these methods can be used to produce rankings which are interpretable as measures of accessibility where the objects in the sets are potential destinations in a transport network. One limitation of these methods is that they take no account of the degree to which objects in a set are similar or otherwise. To address this limitation the concept of diversity is introduced. Several methods of measuring diversity proposed in the literature are then examined which are distinct from but which have clear conceptual links with accessibility. A method of measuring diversity which incorporates both spatial and non-spatial components is then proposed.
In the second part of this paper, households' willingness to pay for diversity of opportunity when choosing a residential location is estimated, with a specific focus on diversity of access to food shopping. A panel of 100 respondents were asked to undertake a stated preference experiment as part of a web-based questionnaire. Each respondent was presented with 9 scenarios. In each scenario respondents were invited to choose between two alternatives characterised by attributes reflecting different levels of monthly household cost, travel time to work, housing density as well as diversity of access to food shopping.
Association for European Transport