What factors affect the match rates of police and emergency department data in Sweden’s road traffic crash database Strada?

Data linkage between police and hospital datasets is valuable for understanding both the circumstances and injury outcomes of road traffic crashes. The key to correct usage of linked datasets, on which to base effective interventions, is understanding what factors affect the proportion of records matched between datasets (the match rate). This study investigates which factors affect the match rates of police and emergency department (ED) data in Sweden’s crash registry, Strada. Both the police and all EDs in Sweden report directly to Strada. The EDs provide both AIS-coding of injuries and information on crash circumstances, and filed reports are matched with police reports continuously. As such, this study also aims to provide insights into this national data linkage system that is essentially real-time. Based on data from 2022 to 2023, logistic regression is used to analyze the match rates considering injury severity, sex, age group, road user category, and county. The results show a higher overall police match rate of 0.345 compared to an overall ED match rate of 0.197, largely due to police capturing fewer single-bicycle crashes. Higher match rates for police reported motorcycle riders and lower match rates for both police and ED reported bus occupants are also found. Furthermore, higher injury severities are associated with higher match rates. The results also show large differences between counties, highlighting that results from previous studies with narrower geographical focus may not be transferable, not even within the same reporting system and country.