Anxiety research is conducted within two separate traditions: (a) as an acute emotion and as a personality construct, and (b) as a mental disorder or an illness. The first line of research is mainly done by psychologists based on psychometric tools with a major focus on individual differences. The second line of research is mainly done by psychiatrists based on qualitative categories (such as given by the DSM) with a focus on case studies.
A distinction between state and trait anxiety has become commonplace (Spielberger, 1972, 1983). State anxiety is defined as an unpleasant emotional arousal in face of threatening demands or dangers. A cognitive appraisal of threat is a prerequisite for the experience of this emotion (Lazarus, 1991). Trait anxiety, on the other hand, reflects the existence of stable individual differences in the tendency to respond with state anxiety in the anticipation of threatening situations.
Moreover, at the level of both state and trait anxiety, a further distinction has been made between worry and emotionality (Spielberger, 1980). Worry refers to the cognitive component of the anxiety experience. Individuals respond to threat with worries about the imminent danger and their perceived lack of competence to counteract the threat.
Among many instruments to assess anxiety, one stands out: the State-Trait Anxiety Inventory (STAI, Spielberger, 1983). This does not mean that it is an ideal measure but it is the most frequently used scale in research world-wide, and no other measure has received as many foreign language adaptations and citations in the last three decades. Thus, it is the standard in the field. The self-report inventory consists of 20 items to assess state anxiety, and another 20 items to assess trait anxiety.