An understanding of the relative benefits of ALS and BLS OHCA care is extremely important, potentially guiding community EMS system design and resource investment. For example, the duration of advanced level paramedic training in the US is ten fold higher than that required for basic level emergency medical technicians. Recent studies raise questions about the clinical value of ALS in OHCA care, suggesting that these interventions offer no additional survival benefit over basic measures. However, these prior analyses contain some limitations, including the use of before-after study design or reliance up on hospital based administrative data to infer the nature of care delivered by EMS.