A power calculation has been made, based on this distribution and the assumption that a clinically relevant difference, is defined as any time interval in cases considered as having a high on-scene-time, (>15 min.) being twice the amount than in cases considered as having a low on-scene-time (≤15 min.). This has shown an estimated demand of 500 registration forms in order to achieve a power of 0,8 with a 5% two-sided confidence interval.