The spread of certification programs and the adoption of the principles defined in the “Mobility Charter” have led more and more Public Transport companies to undertake evaluation procedures, not only for effectiveness and efficiency, but more generally for quality improvement.
The issue of evaluating public transport services presents a remarkable complexity since the evaluation process requirese to take into consideration the perspectives of the different stakeholders: on one side the company managing the service and on the other the users and/or the community directly or indirectly concerned in.
The use of statistical methodologies for assessing and analyzing Passenger Satisfaction (PS) is a fundamental task to derive the information necessary to support strategic decisions.  It should be stressed that the assessment of quality of services is an extremely complex task as they are intangible and heterogeneous.
Direct involvement of the service beneficiary leads to evaluate quality not as an objective characteristic, not to mention that the users’s expectations have radically changed and are nowadays based on the construction of the individual relationship with the new technologies.
In addition, the quality of service produced by a public transport system is characterised by many factors that transform it into a multi-dimensional phenomenon.  In almost all statistical studies on PS problem, data are presented on an ordinal scale, therefore statistical tools must be able to take all these aspects into account.