* A novel paper generated news headlines in December 2022. It tried to evaluate if COVID vaccination was associated with the risks of a traffic crash.
* The hypothesis being tested was that people who ignore public health messages might ignore road safety guidelines.
* The study was large (over 11 million people). It was conducted in Canada.
* There were 6,682 traffic crashes during the study, which was just one month long (August 2021).
* Most people, 84%, had received a COVID vaccine. It was claimed that unvaccinated people had a 72% increased relative risk of a traffic crash compared with those vaccinated.
* Unvaccinated people were more likely to be younger, male and of lower socioeconomic status. None of these were adjusted for in that 72% claim.
* After adjustment, the relative risk figure became 48%. However, there were two further issues 1) important factors that weren't adjusted for (e.g., driver ability, personality traits etc.) and 2) a number of conditions were adjusted for that weren't crash risk factors but did counterbalance the age issue.
* The twist in the paper was that only 43% of the crashes involved drivers. The other 57% involved passengers or pedestrians. The hypothesis surely only holds for drivers.
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