Box plot showing distribution of the absolute standard mean differences for the raw data compared with PSM, PTW, and entropy balancing. Each comparison group is represented by high-dose vs nonvaccinated (A), high-dose vs standard-dose (B), and standard-dose vs not vaccinated (C). The first panel represents the 2016–2017 season, the second panel represents the 2017–2018 season, and the last panel represents the 2018–2019 season. Abbreviations: IPTW, inverse probability treatment weighting; PSM, propensity score matching.