# Modeling Public Transportation Use Among Short-Term Rental Guests in Madrid
## 2 Materials and Methods
### Survey  
According to the first step of the explained workflow, a structured survey campaign was conducted to characterize the behavior of individuals staying in tourist accommodations in Madrid. To enable direct, face-to-face administration of the questionnaire, management companies overseeing short-term rental properties were engaged with. In contexts where in-person check-ins took place, these companies facilitated immediate guest contact, yielding a high response rate. In parallel, hourly luggage-storage services (\"lockers\"), commonly utilized by visitors residing in tourist homes, were identified as an additional distribution channel; certain locker operators provided on-site personnel who could approach and invite customers to participate. In total, three short-term rental property management firms (Minty Host S.L., Apolo Homes S.L., and The Key Host S.L.) and one locker service provider (Lock & Be Free S.L.) agreed to participate in the survey campaign.  
A structured survey was conducted over an eight-month period, from January to April 2024 and from September 2024 to December 2024. The reference population for sample  
Figure 1: Methodological workflow.  
size estimation comprised all tourists who stayed in Madrid's tourist accommodations, an annual total of approximately two million visitors, according to 2019 AirDNA data. Sample-size calculations employed a conventional formula for proportion estimates, with the following parameters: event probability (\(p\) = 0.05), complement probability (q = 0.95), significance level (\(\alpha\) = 0.05, yielding Z = 1.96 for a 95% confidence interval), and margin of error (d = 0.025). Although this calculation suggests that around 400 completed surveys would be sufficient for estimating proportions with the specified precision, a larger overall sample was targeted. This decision was made to ensure sufficient representation of tourists staying in peripheral areas of the city, who are known to represent a relatively small proportion of the total population. A larger sample improves the reliability of estimates for such subpopulations.  
The survey instrument was developed in English and Spanish and comprised three sequential sections. The first section elicited respondents' socioeconomic and stay-related characteristics, including age cohort, country of origin, party size, the inclusion of elderly or minor travelers, location of the accommodation, primary travel purpose, whether the visit constituted a first-time stay in the city, length of stay in nights, and the principal points of interest (POIs) visited. The second section examined urban accessibility and mobility behaviors by quantifying public transport usage across modes and soliciting overall service-quality ratings; it also asked respondents to rate the importance of proximity to airports, major rail stations, metro stations, and urban bus stops in their choice of accommodation. The final section assessed tourists' expenditure patterns within short-term rental contexts, requesting an estimate of the total non-accommodation budget and the percentage allocation of these funds to food purchases, souvenir or gift acquisition, and dining at establishments in the immediate vicinity of the rental property.