Linking EMS and In-Hospital Stroke Records: Impact of Deterministic vs. Probabilistic Methods on Selection Bias

Background Linking emergency medical services (EMS) and hospital stroke registry data is crucial for evaluating stroke systems of care, but the impact of different linkage methods on selection bias remains unclear. This study compared deterministic and probabilistic linkage approaches and assessed their effects on sample representativeness and analytical conclusions

In this cross-sectional study we analyzed 13,567 stroke patients transported by EMS to 40 Kentucky hospitals participating in Get With The Guidelines – Stroke (2021-2023). Records were linked using deterministic and probabilistic methods. We compared match rates, assessed sample representativeness, and evaluated the impact of selection bias using inverse probability weighting.

Deterministic and probabilistic methods achieved match rates of 73.0% and 78.7%, respectively. Both methods produced similar representative samples, with modest differences between matched and unmatched cases primarily in race and admission year. Accounting for selection bias had minimal impact on the estimated associations between EMS stroke recognition and outcomes (percent change in adjusted odds ratios < 1%).

While probabilistic linkage yielded modestly higher match rates, both methods produced comparable results with minimal selection bias. When working with high-quality data with low missingness, deterministic linkage may be sufficient for many analyses, though sensitivity analyses remain important for assessing potential bias. Competing Interest Statement The authors have declared no competing interest. Funding Statement This study was supported by the US Centers for Disease Control and Prevention as part of the Paul Coverdell National Acute Stroke Program (NU58DP006953). Get With The Guidelines-Stroke is funded by the American Heart Association and the American Stroke Association. Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Not Applicable The details of the IRB/oversight body that provided approval or exemption for the research described are given below: University of Kentucky Office of Research Integrity I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Not Applicable I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Not Applicable I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Not Applicable Data Availability Data for the current study are not publicly available due to data sharing agreements between participating hospitals and American Heart Association data use restrictions.