Quality of Service (QoS) in digital television broadcasting has been the subject of many studies during the last decade. This has led to the establishement of various standards and recommandations by organisations such as ETSI and the ITU. More than twenty relevant parameters and associated measurement methods have been specified by ETSI for DVB but their interpretation, usage and exploitation are often considered "difficult" - in that they require a high level of expertise. This article describes how three "synthetic" parameters have been developed to make assessment of QoS considerably easier. They could represent the keystone of QoS in digital TV services.