Study objective: Measurement of interval data is important in the accurate recording of events that occur in an emergency medical services system. Measurement of intervals should be a simple task. However, when two separate clocks are needed to record the beginning and end of an interval, accurate measurement may be difficult. We sought to accurately measure the 911 call receipt-to-vehicle departure and 911 calls receipt-to-patient access intervals in a system with primary and secondary public safety answering points (PSAPs).
Methods: We conducted a descriptive study between January 1 and July 31, 1993. All 911 calls beginning at the primary PSAP, transferred to the EMS secondary PSAP, and ending with patient access times were eligible. Clock-synchronization errors and unavailability of 911 time logs were the criteria for exclusion. We measured the 911 call receipt-to-vehicle departure interval by adding the primary-PSAP and the EMS secondary-PSAP call-processing intervals. The 911 call receipt-to-patient access interval was the absolute difference between the time when the 911 primary-PSAP phone range and the time of patient access recorded by EMS personnel.
Results: The data were best described with median and interquartile ranges (IQRs). We found 1,945 calls that met inclusion criteria. Of these, 270 were deleted because of clock errors and 616 for time log unavailability, yielding 1,059 calls for interval determinations. The median 911 call receipt-to-vehicle departure interval was 1.7 minutes (IQR, 1.2 to 2.2 minutes). The median 911 call receipt-to-patient access interval was 8.2 minutes (IQR, 6.4 to 10.5 minutes).
Conclusion: The 911 call receipt-to-vehicle departure and 911 call receipt-to-patient access intervals can be accurately measured in a system with two separate PSAP computer-aided dispatch clocks. These intervals are variable and often lengthy.