Collective depression is one of many collective mental states, such as collective elation, collective paranoia, collective trauma, or collective grief, which may affect a group, community or whole nation. It is characterised by a prevailing and seemingly permanent sense of inadequacy, despondency, lack of vitality, sadness and hopelessness, shared by a high proportion of the members of a collectivity. As shown by Gustave Le Bon in 1895, it can be passed by contagion, in a way similar to a physical condition.