The Influence of Operational Exposure on Scene Time Agency Call Volume and the Compression of On-Scene Time Variability in Emergency Medical Services
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Abstract
A limited number of emergency medical services (EMS) agencies respond to a disproportionate share of all 911-initiated calls in the United States. This study tests the hypothesis that responding units operating within high-volume service areas exhibit shorter and more consistent on-scene times for most call types than units serving lower-volume areas.
This study uses patient care report data generated from EMS providers whose agencies then contribute these reports to the national repository, the National Emergency Medical Services Information System (NEMSIS). The repository publishes data on a yearly basis. A random sample was drawn from approximately 262.7 million records between 2017 and 2023 to create a dataset of over 232,000 records for hypothesis testing. The data reveal a profound inequality of workload in that a relatively small number of agencies from across the country are responsible for handling the vast majority of all 911 calls represented in the sample. Of 7,536 agencies appearing in the nationwide sample, only 75 agencies (~1%) handle 30% of all calls, which is nearly twice the volume of the 6000 least busy agencies put together. Exceptionally busy agencies post faster scene times on average, and these effects survive multivariate analysis. Busy agencies are also less likely to exhibit extreme delays in scene times – keeping their scene times within a narrow and predictable range. No agency in the top 20% busiest by call volume had an agency-level median scene time exceeding 26.7 minutes. Connecting deidentified agency-level codes to each report further permits consideration of high call volume as a possible proxy for experience at the agency level.
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