Empirical Analysis of Ambulance Travel Times: The Case of Calgary Emergency Medical Services
利用加拿大卡尔加里市高优先级呼叫的行政数据，研究救护车行程时间与距离的关系，发现对数变换使时间分布对称且尾部更厚，并提出了变异系数随距离递减的新模型，可用于绘制覆盖概率图以改进系统绩效。
Using administrative data for high-priority calls in Calgary, Alberta, we estimate how ambulance travel times depend on distance. We find that a logarithmic transformation produces symmetric travel-time distributions with heavier tails than those of a normal distribution. Guided by nonparametric estimates of the median and coefficient of variation, we demonstrate that a previously proposed model for mean fire engine travel times is a valid and useful description of median ambulance travel times. We propose a new specification for the coefficient of variation, which decreases with distance. We illustrate how the resulting travel-time distribution model can be used to create probability-of-coverage maps for diagnosis and improvement of system performance.