Valuation of Aircraft Noise Using Stated Preference Methods Within a Broader Quality of Life Dimension
M Wardman, A Bristow, ITS, University of Leeds; P Murphy, C Heaver, FaberMaunsell, UK
One of the main advantages of Stated Preference (SP) over the cruder Stated Intentions and Willingness to Pay approaches is that the range of variables included makes the true purpose of the study less apparent, thereby offering a lesser invitation to response bias. There is, however, a widely held view that SP exercises should be kept as simple as possible in order to obtain reliable responses. This prevailing view, although regarded to be ?urban myth? by some practitioners, has resulted in a trend towards SP exercises with fewer variables.
Our opinion is that in many circumstances where alternatives are represented by only a few attributes, the purpose of the SP exercise will be quite transparent. It is likely that the invitation to strategic bias and protest responses that this offers is the cause of the often implausibly high values of crowding related variables (Fowkes and Wardman 1987) and rolling stock improvements (Wardman and Whelan, 2001). Indeed, the latter study found that SP based valuations were three times higher where it was felt that the study would be readily perceived to relate to new trains.
In this study we were interested to value aircraft related noise. What would have been a ?naïve? approach would have simply offered choices between alternatives described in terms of noise levels and some form of monetary variable. In such cases respondents would be aware that the purpose of the study was to evaluate changes in aircraft noise rather than changes in council tax. We would therefore expect such an SP exercise to produce inflated values of aircraft noise in an attempt to influence policy makers. The arguments are analogous to those used to explain why the willingness to pay method obtains too high values of public goods where actual payment is unlikely (Bohm, 1971).
This paper reports the results of research which is innovative both in the form of the SP method used and in the range of issues to which it has been applied. A series of focus groups revealed that quality of life issues which included aircraft noise could be raised with residents around airports without raising suspicion that the survey was specifically about aircraft noise. It was only when very specific aircraft related issues were covered, such as attitudes towards aircraft movements and the simulation of aircraft noise, that group members were alerted to what the study was about.
In order to disguise the purpose of the SP exercise, respondents were asked to consider a range of quality of life attributes. These were the level of local crime, street cleanliness, the quality of local schools, the amount of road traffic in the area, road traffic noise experienced at home, neighbourhood air quality, aircraft noise, the condition of roads and pavements, the availability of local recreation, shopping and health facilities and the level local council tax. Most attributes were specified at five levels, with respondents identifying the level of each that they currently faced and hence the worse and better levels of each attribute. The respondent is then first asked which improvement would be preferred. Once this is identified, the improvement is removed from consideration and the respondent is asked which of the remaining improvements is preferred, with the current situation remaining as the reference point for all other variables. This process is continued until all the improvements are evaluated. The deteriorations are then evaluated in the same way. The choices made by individuals have been modelled using an exploded logit procedure, with jack-knifing used to correct for repeat observations.
This approach has its background in the priority evaluator approach used to address quality of life issues (Hoinville, 1971) and subsequently widely used in the rail industry in Great Britain to value ?soft? variables. However, the approach of allocating a ? points budget? amongst competing improvements each of which have ?point prices? builds in linear-dependency amongst the attributes that characterise the alternatives between which the individual implicitly chooses.
Data collection was completed in late 2002, with 600 completed interviews of residents around Manchester, Bucharest and Lyon airports. The results of the study are to be reported to Eurocontrol, who have funded the research, in February. Initial results are promising, with correct sign and significant coefficient estimates obtained for improvements to the current situation.
This paper will deal with the methodological issues involved in this approach, and in particular will test the hypothesis that it produces lower values of aircraft noise than a naïve SP approach. The results will also be compared with respondents? importance and satisfaction ratings of each attribute whilst valuations of a range of other quality of life related attributes will be reported.
Bohm, P. (1971) An Approach to the Problem of Estimating Demand for Public Goods. Swedish Journal of Economics, 73(1).
Hoinville, G. (1971) Evaluating Community Preferences. Environment and Planning 3, pp.33-50.
Fowkes, A.S. and Wardman, M. (1987). The Values of Overcrowding and Departure Time Variations for Inter City Rail Travellers. Technical Note 229, Institute for Transport Studies.
Wardman, M. and Whelan, G. (2001) Valuation of Improved Railway Rolling Stock: A Review of the Literature and New Evidence. Transport Reviews, 21 (4), pp.415-448.
Association for European Transport