[Analysis of parameters used for the evaluation of the Relative Complexity Index beta]. 
The Relative Complexity Index beta (RCI beta) has been devised as an indicator of the relative complexity and cost of anaesthesia.  It takes into account the type of anaesthesia, the duration, the type of surgery and the patients' ASA status.  This study analyses the relative weight of each component of RCI by a multiple regression analysis.  The results show the pre-eminence of the surgical procedure in the formula.  The weight of surgical procedure is responsible of 80 p. cent of the model's variance.  In these conditions, the RCI beta cannot be accepted as an accurate complexity index of anaesthesia.