In 1997, after the death of Princess Diana, the British popular press declared that Britain was having a "collective nervous breakdown". This paper considers whether it is possible to assert that a collective mental state could exist, such that it could have a "breakdown" (to use a non-technical term). In reality, the concept of the collective mental state has a long history, but it also has a well-known critique called Methodological Individualism, where thoughts and actions can only be attributed to individuals. If the concept of the collective mental state is valid, then it is possible to argue that the normal functioning of a group, community, or whole society, that is, a collectivity, can be disrupted by contagion, and that it can be said to be disordered. Some of the common large-scale disorders that have been recognised are depression, fear, aggression, desensitization and acceptance of genocide. Thus, the concept of the collective mental state can provide a valuable transdisciplinary vehicle for the investigation of some of the great issues confronting humankind.

This paper is on the development of a theoretically based national identity measure. Two empirical studies with 200 participants were carried out to show that the more generally conceptualised Collective Self-Esteem Scale (CSES) by Luhtanen & Crocker (1992) provides indeed a proper base to aim at a more specific measure of national identity. However, in order to really include all those crucial aspects which, according to Social Identity Theory (Tajfel & Turner, 1986), seem necessary in defining a collective identity like the national one, the scale was completed by the aspect of comparison-torelevant-outgroups. In fact, this completion led to a substantial increase in variance explained by the new scale compared to the CSES. 6 tables and 1 picture give detailed information about respective data patterns.