Response Willingness in Consecutive Travel Surveys

Response Willingness in Consecutive Travel Surveys

Principal Investigator: Patricia L. Mokhtarian, Susan G and Christopher D Pappas Professor, School of Civil and Environmental Engineering
Co-principal Investigator: Kari E. Watkins, Frederick Law Olmsted Associate Professor, School of Civil and Environmental Engineering
Project Duration: 12 months
​Project Budget (Federal UTC Funds): $109,458
Project Budget (Cost-share): $54,791
Institution: Georgia Institute of Technology

Declining survey response rates have increased the costs of travel survey recruitment. Recruiting respondents based on their expressed willingness to participate in future surveys, obtained from a preceding survey, is a potential solution but may exacerbate sample biases. In this study, we analyze the self-selection biases of survey respondents recruited from the 2017 U.S. National Household Travel Survey (NHTS), who had agreed to be contacted again for follow-up surveys. We apply a probit with sample selection (PSS) model to analyze (1) respondents’ willingness to participate in a follow-up survey (the selection model) and (2) their actual response behavior once contacted (the outcome model). Results verify the existence of self-selection biases, which are related to survey burden, sociodemographic characteristics, travel behavior, and item non-response to sensitive variables. We find that age, homeownership, and medical conditions have opposing effects on respondents’ willingness to participate and their actual survey participation. The PSS model is then validated using a hold-out sample and applied to the NHTS samples from various geographic regions to predict follow-up survey participation. Effect size indicators for differences between predicted and actual (population) distributions of select sociodemographic and travel-related variables suggest that the resulting samples may be most biased along age and education dimensions. Further, we summarized six model performance measures based on the PSS model structure. Overall, this study provides insight into self-selection biases in respondents recruited from preceding travel surveys. Model results can help researchers better understand and address such biases, while the nuanced application of various model measures lays a foundation for appropriate comparison across sample selection models.

Research Products and Implementation

Scope of Work

​Final Report