# Mode Choice Effects on Bike Sharing Systems
## 3 Survey Design and Choice Experiment
### Revealed and Stated Preferences: Survey Protocol  
Choices on, e.g., transport modes and routes can be observed either in real-life situations or in hypothetical choice situations. Real-life observations result in information on revealed preferences (RP) whereas observations of hypothetical choices result in data \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{2}{c}{**Subsample 1: BSS-Users**} & **Subsample 2: BSS Non-User** \\ \hline Frame-population & Users of BSS VRNnextbike & BSS non-user residents from VRNnextbike \\ Recruitment & Via the nextbike app at the start or end of bike-rent & supply area \\  & Computer-assisted telephone interviews (CATI) and & Recruitment call via telephone \\ Survey mode & paper-and-pencil questionnaire with a postpaid & Paper-and-pencil questionnaire with a postpaid \\  & return envelope & return envelope \\ Incentive & EUR 20 after participation in the CATI and again & EUR 20 after returning the \\  & after returning the filled-out questionnaire & filled-out questionnaire \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Frame population and recruitment strategy. on stated preferences (SP). RP data have the advantage of representing peoples' actual behaviour; they, however, also include disadvantages such as little variation in attributes, which could be used to explain choices (e.g., travel times by bus on a specific route), and issues of multicollinearity (e.g., travel times, distances, and costs are often highly correlated for a specific transport mean). In addition, future effects, demands, and supplies cannot be addressed with RP data. SP and according to hypothetical choices overcome these issues. Here, an experimental design is employed, that focuses on selected and potentially future attributes. It asks respondents to exclusively consider these selected effects when making their choices. Attribute variation is controlled by an experimental design, which allows overcoming the challenge of multicollinearity. The disadvantages are, however, the hypothetical character of the choice tasks and the reduction of complexity (for a more detailed discussion on RP- and SP choices see, e.g., Refs. [19, 28, 29]). In transport planning, RP and SP data are often combined to overcome the mentioned limitations of the SP approach. One way to increase the reliability of SP choices is to employ an individual's RP decisions as the basis for her or his SP-choice situations [30] (for a discussion of combined RP-SP studies see Ref. [19]). This means, on the one hand, an increased complexity for the fieldwork, as choice situations are individually tailored for each participant of the SP survey. On the other hand, the RP-SP combination increases the quality of a survey as the choice situations are based on former choices of a respondent, transport familiarity and thus allow an easy imagination of the choice situation under observation. The more realistic and familiar a choice situation is, the less effort it takes to be contextualized resulting in more reliable respondents' answers (for choice situations see Ref. [31]; for a more general discussion on response burden see Ref. [32])  
In the CATI for BSS-users, information on mobility-tool ownership, trip characteristics of the BSS-use at the time of recruitment, attitudes on BSS, and socio-demographics were collected. During the interview, the chosen route of the rental bike trip was traced electronically by employing an online routing tool [33] to gather additional information for the trip, such as travel time and road surface. The collected information and RP data were employed as a basis for the mode choice experiment. Based on these BSS attributes, trip characteristics for the alternative modes PT and PMT were collected using an online routing provider [34] and an electronic PT-schedule service [35]. The choice experiment itself was designed as a follow-up survey and presented to those CATI participants, who agreed in filling out the paper-and-pencil questionnaire.