The influence of SP design on the incentive to bias in responses

This paper reviews and explores incentives for respondents to bias theirstate of preference answers, such as strategic bias, affirmation bias, and status quo bias etc. Through investigating the effects of biases, the paper aims to find the influence of different design on responses, and try to find methods to reduce biases caused by the design and practice of SP experiments. In an empirical demonstration using data obtained from 1221 commuters on the valuation of new rolling stock in Greater Manchester, UK, this paper presents results for different designs. The aim is to help SP designer and practitioner to reduce biases, and improve the validity and reliability of SP results. In previous studies, SP was found to be the most reliable method to investigate the service quality improvements. Some reviews on the SP application to rolling stock studies found the monetary valuesfor time and frequency derived from SP methods have been remarkably consistent among studies. However, the valuation of soft variables such as service quality (rolling stock, punctuality, crowding and so on) is rather less convincing. This can be explained as the bias by which respondents overestimate the value of those characteristics to improve their well-being or by packaging effects. As a result, SP models have been observed to producedemand forecasts or values which are too high, and bias has been found. After a review of studies on rolling stock in recent years, an SP experiment has been designed to investigate the effects of different designs on responses. Two factors were introduced into the experiment, 'Cheap Talk' and 'Masking the Aim of Experiment', to amend the incentive to bias. Cheap Talk is a term used in the Contingent Valuation Methods where a proper designed Cheap Talk has been shown to reduce the strategic bias. Simply put, Cheap Talk (CT) is a warning message before the survey that tells respondentswhat caused biases in previous experiments. A pilot survey was conducted in August 2005 followed by the main survey from November to December 2005 in Greater Manchester. Four groups of questionnaires which include the above two factors separately and together. A total of 2768 paper-based questionnaires were sent out. 1321 commuters mailed back, of which there were 1221 usable questionnaires. For these 1221 commuters, both 'Cheap Talk'and 'Masking the Aim'are seen to have some significant effects on the SP responses and the results estimated to them. For the covering abstract see ITRD E135582.


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Filing Info

  • Accession Number: 01089885
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • ISBN: 1905701012
  • Files: ITRD
  • Created Date: Mar 17 2008 10:10AM