Stated Preference - or `SP` - grew out of Conjoint Analysis, which was originally developed by market researchers and psychologists in the US during the 1970s. Its use in transport grew rapidly in the 1980s and 1990s, and now it is one of the most widely used techniques in the transport planner`s toolkit.

SP is concerned with understanding people`s preferences, and how they use those preferences to make choices. In transport we need to understand and quantify the importance people attach to the `attributes` of travel, and how changes in those attributes might affect what they do. Such attributes include things like travel time, service frequency, walk times and fares, but SP can also be used to look at more subtle things, such as the type of vehicle being used, the quality of ride or the service reliability.

The results of a Stated Preference survey are usually used in one of two ways:

• to provide measures of the importance people attach to changes in attributes. These are often given in terms of money - people`s willingness to pay for improvements - and these monetary values can be used in economic appraisal to calculate the consumer surplus associated with a proposed investment
  
• to provide forecasts of how people will make choices in future if new services are introduced, or existing ones changed. Although this can be done directly from SP results, it is more usual - and better practice - to do it using more complete models, such as transport network models.

What is it?
SP is a survey technique. People are interviewed, and we play `games` with them, in which they are asked to make choices between alternative services or products. By varying the values of the service attributes - cost, time etc - in a carefully controlled way, we can learn about how much importance people attach to them on the basis of the choices they make.



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