Formal clinical characteristics of delusional beliefs.

We studied 13 formal clinical characteristics of delusions by means of observer-rated ordinal scales in a sample of 74 psychiatric inpatients with mainly schizophrenic or schizophreniform disorders. The interrater reliability of the scales was found to be satisfactory. High levels of conviction about their truth and to a lower extent lack of dismissibility and lack of resistance against them were found to be the hallmarks of delusional beliefs. The lack of strong intercorrelations among the scales items supports the hypothesis that the concept of delusions represents various aspects of delusional experience which are relatively independent of one another.