Substantive and methodological issues in a rating of cognitive and psychological function in multiple sclerosis.

There is a need for a practical, reliable, and valid rating scale for cognitive function in Multiple Sclerosis due to the high frequency of cognitive dysfunction and its consequences for patients and family. The process of rating cognitive function is examined from the point of view of the observer, the observed, and the examination and rating scales. It is concluded that observers can be trained to reduce bias and increase reliability. The patient may be a source of information through diaries, check lists, and interviews. Rating items must be based on the major cognitive deficit factors in multiple sclerosis. Standardized examination must be the basis for ratings. Rating items must be clear and closely tied to observable behaviour. A series of steps for a project to develop an acceptable international cognitive rating scale is proposed.