The Vigilance Scale: an analysis of elicited behavioral responses.

The Vigilance Scale (VS) is a 12-step additive (Guttman scale) that allows assessment of the behavioral deficit in the unconscious state and the state of clouding of consciousness. Despite restrictions on its applicability, which are discussed in detail, the VS seems to be a useful measuring device that indicates the level of brain function a patient with a disturbance of consciousness can actually attain. There are two categories of scale errors to be found, the first being caused by various "instrumental" disorders, i.e., severe motor deficits, the second resulting from the probabilistic approach of the VS to a Guttman scale.