The Distributional Impact of Fatigue on Performance

44 Pages Posted: 18 Nov 2021 Last revised: 24 Aug 2022

See all articles by Hessam Bavafa

Hessam Bavafa

University of Wisconsin - Madison - School of Business

Jónas Oddur Jónasson

MIT Sloan School of Management

Date Written: October 15, 2021


Little is known about how people-centric factors affect the shape of service time distributions, despite distributional statistics (variance or quantiles) being key drivers of system performance in many service industries. We investigate the impact of one people-centric factor--worker fatigue--on the average, variance, and quantiles of service times in paramedic operations. Our analysis uses data on the performance of 368,634 paramedic teams in the London Ambulance Service over 10 years. We measure fatigue by the number of prior jobs a paramedic crew has completed during a shift and estimate its impact on the time it takes the crew to respond to incidents and bring patients to hospitals. Using a re-centered influence function regression approach with multiple fixed effects, we find that the average time to hospital increases by 5% throughout the course of an average shift. In addition, the workers become less consistent with fatigue: service time variance increases by 39% during a normal shift. Furthermore, we find that in addition to an upward shift in mean service times, both the upper and lower tails of the distribution have more weight for fatigued paramedics. These effects are mostly driven by the performance of paramedics at the scene, rather than their driving to or from the incident. The distributional effects of fatigue are only slightly mitigated by increased experience or reduced system workload. Our work demonstrates that the impact of people-centric factors can be highly non-uniform across the service time distribution.

Keywords: Fatigue, Service Time Distribution, Performance Consistency, Variability, Operational Performance, Service Operations, Ambulance Operations

Suggested Citation

Bavafa, Hessam and Jónasson, Jónas Oddur, The Distributional Impact of Fatigue on Performance (October 15, 2021). Available at SSRN: or

Hessam Bavafa

University of Wisconsin - Madison - School of Business ( email )

975 University Ave
4284C Grainger Hall
Madison, WI 53706
United States

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Jónas Oddur Jónasson (Contact Author)

MIT Sloan School of Management ( email )

100 Main Street
Cambridge, MA 02142
United States

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