<qa>  What is the primary outcome measure of mortality?Methods: The Pediatric OPALS Study will incorporate a before-after design with the unit of study being all eligible patients seen during each of two distinct 36-month periods in 17 Ontario cities. During the baseline Control Before Period 1992-1998, the study cities provided BLS-D level of care with first-responder firefighters and Primary Care Paramedics. During the Intervention After Period 1998-2002, the study cities provided a full pre-hospital ALS program. The study population is all patients under the age of 16 years who were treated out-of-hospital for any of these four conditions: a Respiratory Distress or Obstruction, defined as patients with a chief complaint of shortness of breath, respiratory arrest, or airway obstruction; b Seizure, defined as patients having suffered a generalized convulsion; c Major Trauma, defined as patients with injuries caused by any mechanism and associated with an Injury Severity Score ISS more than 12; d Cardiopulmonary Arrest, defined as patients with absence of a detectable pulse, unresponsiveness, and apnea. The study intervention was implemented during the Run-in period, immediately prior to the Intervention period, and entails a program of pre-hospital ALS care provided by EMS: a Endotracheal Intubation, b Intravenous therapy, and c Administration of intravenous drugs. Study cities had to meet four strict performance criteria. Data will be obtained by electronic or hard copy means from the following sources: Ambulance Call Reports, Fire Medical Reports, Base Hospital Reviews, Ambulance Response Information System, Hospital Records, Ontario Trauma Registry, and Follow-up Interviews. The primary outcome measure will be mortality. Secondary outcomes include a Other Clinical Measures Other Survival, Need for Interventions in the ED, Admission, Lengths of Stay, b Generic Quality of Life HUI3, c Disease-specific Quality of Life CPC, FIM, d Response Time Intervals, and g Direct Costs. The primary data analysis will test the hypothesis that mortality discharge will be improved when comparing the after period to the before period by chi-square analysis techniques. Stepwise logistic regression analysis will be performed to control for the possible confounding effects of various indicators and to assess the effect of the study period on survival. The study will involve a total of 18,000 pediatric patients over 72 months. 