Audio-based choice set layout

In a choice modelling survey questionnaire, respondents are presented with a series of choice sets illustrating different policy options. The layout of these choice sets should clearly describe the levels of each alternative to the respondents. Previous choice modelling survey questionnaires have used tables with different levels associated with each attribute to illustrate each policy option.

The choice sets used in audio-based survey questionnaires depart from previous choice modelling surveys as recorded noise was played to respondents as part of the survey, necessitating presentation of both audio and textual information to the respondent. Consequently, the survey cannot be conducted on pre-built survey platforms (e.g., Google Forms and Survey Monkey) as these survey platforms do not have the flexibility to include sound clips into the choice sets. As such the survey questionnaires were coded in hypertext mark-up language (HTML) and JavaScript to allow for flexibility in the choice set design.

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The design of the choice set for textual information was similar to other choice modelling surveys and the text was presented in a table format detailing the different levels for each attribute. However, the audio recordings could be presented to respondents in a variety of different layouts. Two options to present the audio recordings involved a stand-alone audio player (Figure 5-3), and embedding the audio clip into the table containing the textual information for other non-audio attributes49 (Figure 5-4).

Figure 5-3 Preliminary design of choice set with an audio player

49 _{A sample of the choice card with embedded audio recordings, which was eventually used in the finalised survey}

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Figure 5-4 Preliminary design of choice set with embedded audio

There were pros and cons associated with both layouts. A key advantage of the stand- alone audio player was ease of coding. Preparation of this choice set was straightforward as pre-programmed JavaScript libraries can be used to design the choice set and extensive coding was not required. By comparison, embedding audio into the choice set was more complex and required more extensive coding. Details on the coding of the choice set with embedded audio were provided in Appendix 1.

Notwithstanding the difficulties with programming the choice sets, embedding the audio clips into the choice set made it easier for respondents to make their choice. When the audio clip associated with each option was playing, the row of the table was highlighted, clearly indicating the alternative that is associated with the clip. Hence, respondents were able to see the audio clip associated with each option. This reduced the effort of having to scroll to the audio player to hear the recording. Ease of use is important in the survey as respondents were required to complete eight choice sets over the course of the survey. As such, a more readily

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understandable layout of the choice set was preferable to a choice set that was more easily programmed. Both choice set layouts were pre-tested during the focus group discussions.

The choice set was designed to fulfil several criteria. First, the audio was calibrated to ensure that the sound pressure level perceived by respondents is equivalent to the design level of noise. For instance, if an alternative in a given choice set is designed to contain a noise with a loudness of 70dB, the sound played by the headphones to the respondent was calibrated to be 70dB. Details of the calibration protocol are provided in Appendix 2.

Second, the choice set was designed to ensure that respondents made their choices based on all information provided. In particular, respondents could make their choices without listening to the sound clip if listening to the sound clips is not mandatory. Consequently, at the start of each choice set, a 10-second sample of the noise recording was played to the respondent. The respondent was unable to skip through the playback, ensuring that they heard the recordings of each alternative before they made their choice.

This design increased the duration of the survey. In total, respondents needed to listen to at least 24 audio clips, namely three clips associated with each alternative for 8 choice sets. The total duration of these clips was 4min. However, this increase in the duration of the survey was necessary to ensure that respondents were fully informed about the noise levels associated with each alternative. There was a trade-off between the length of the survey and obtaining more information from each respondent. As the number of choice sets completed by each respondent increased, more information was obtained from each respondent. However, respondents could be fatigued if they were tasked to complete too many choice sets. The number of choice sets used in the survey questionnaire was pre-tested in the focus group discussions.

Third, the choice set sought to contextualise the noise played to respondents.50 This was accomplished with both a description of the noise source as well as a picture of the noise source. The policy context presented in Section 5.3 described the source of noise textually. The textual description was reinforced with a pictorial representation of the noise source on the choice set. The picture of the noise source sought to remind respondents that the noise they were listening to was either from construction sites or roads. Studies from the acoustics literature indicate that

50 _{Ideally, the context of the survey questionnaire should be specific to the noise level at the household. However,}

it was not technically feasible to customise the choice sets at the individual level. Hence, the design of choice set sought to illustrate a typical construction site or road in the pictorial representation.

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visual stimuli can affect the perceived annoyance associated with noise (Cox 2008; Fastl 2004; Menzel et al. 2008). Hence, providing pictures as background to the choice set sought to remove any ambiguity related to the source of the noise.