Flexible monitoring of quality with linguistic control charts

Quality attributes of products and services are frequently assessed using linguistic variables. A method to define innovative control charts for linguistic variables without using any arbitrary numerical encoding is proposed. It is based on the use of the OWA operator (Ordered Weighting Average) introduced by Yager to aggregate information given on a scale where only ordering property applies. A peculiarity of OWA is that the quality inspector is allowed to use a flexible decision logic to face the inherent uncertainty of linguistic assessments. An application to the control of a booking service in a local hospital is presented.