A Pseudo Panel Difference-in-Differences (DiD) Analysis of Online Shopping Behavior in the Puget Sound Regional Council (PSRC) Region

Abstract

Online shopping is a growing trend, particularly following the COVID-19 lock-downs enacted by many cities. Understanding these trends requires robust panel dat methods. However, panel data (i.e., with repeated measurements of the same observational units) are often unavailable. In this study, we use a propensity score weighting (PSW) approach to adjust repeated cross-sectional travel diary surveys collected in the Puget Sound Regional Council (PSRC) region. The most common home delivery is packages (2.09 days per week in 2023), followed by food (0.36 days per week in 2023). We find that single-family detached and townhouse residents tend to receive more home deliveries than those living in apartments. We also find a difference in several patterns pre- and post-COVID pandemic. Vehicle deficient households did not exhibit the same increase in home delivery frequency as other households pre-COVID, but the pattern reversed in the post-COVID period - i.e., vehicle deficient households saw a relative increase in delivery frequency. Overall, this study demonstrates the pseudo-panel approach to causal inference by leveraging differences in PSW-weighted in delivery frequency across treatment groups.