Re: Editorial comment by Dr Menicanti.

[1]  C. Perucci,et al.  Use of hierarchical models to evaluate performance of cardiac surgery centres in the Italian CABG outcome study , 2007, BMC medical research methodology.

[2]  C. Perucci,et al.  Concerning the Editorial comment by Dr Menicanti. , 2006, European journal of cardio-thoracic surgery : official journal of the European Association for Cardio-thoracic Surgery.