While there is considerable evidence in the case of hospitals and surgeons that high volume is associated with better patient outcomes across a variety of medical conditions, to date no study has examined the returns to experience in a pre-hospital setting. Studies of the volume-outcome relation for hospitals and surgeons are plagued by an inherent endogeneity problem; does higher volume raise quality through learning-by-doing, or does higher quality command higher volume through selective referrals? Since ambulance units are dispatched based on proximity and not on reputation, the selective referrals channel at the paramedic level is necessarily shut down. Hence, the only remaining channel for the volume-outcome relationship is learning-by-doing. This paper studies the effect of human capital accumulation through learning-by-doing on performance in the prehospital setting using the universe of trauma-related ambulance runs in Mississippi between 1991 and 2005. In addition, the richness of our data allows us to conduct both individual and firm level analyses, evaluate the contribution of recent versus cumulative experience, study the determinants of firm-level forgetting by separating individual forgetting from labor turnover effects, and the effect of experience on the entire conditional outcome distribution. We find that greater experience is robustly related to improved performance at the trauma scene. However, this benefit operates largely through recent experiences, while the value of more temporally distant experiences depreciates relatively rapidly, suggesting considerable forgetting. For comparability with previous studies, we conduct experiments in which we ignore the paramedic level detail of our data and aggregate volume to the firm level. This understates the benefits of experience, with the estimated firm volume effect being an order of magnitude less than the paramedic-specific effect. One interpretation of this finding is that firm-level volume is a noisy measure of experience. There is also preliminary evidence that individual experience operates not only on mean performance, but also on the upper quantiles of the performance distribution, which can be interpreted as greater experience leading to better standardization with the severity of trauma. As expected, firm level studies, which dominate the literature, focus on firm level interventions by suggesting that large scale effects raise the benefit from consolidation. However, when studying both the individual and the firm, we find relatively small incremental firm scale effects. This suggests that policy and managerial implications regarding human capital accumulation for paramedics should be directed at training, team formation, optimal scale and retention policies as opposed to antitrust and other legislative and regulatory interventions
