BACKGROUND The study sought to investigate the form of the delusion in schizophrenia and the overvalued idea in anorexia, employing a range of belief characteristics to discover whether differences could be detected between them, and how they stood in general relationship to the religious beliefs of normals.
METHOD A belief rating scale was devised with 12 characteristics, and completed by 20 schizophrenics, 20 anorectics, and 20 normal controls. Comparisons were drawn between populations using the Mann-Whitney test, and different types of belief were contrasted within diagnostic groups using each subject as their own control by repeated-measures MANOVA.
RESULTS The schizophrenic delusion was differentiated from the overvalued idea in anorexia by a number of variables, which also served to distinguish both phenomena from religious beliefs held by normals. The schizophrenic delusion exhibited many of the qualities of an initial (or observational) belief, when its content suggested that it should manifest those of a derived belief. The anorectic overvalued idea, although occasionally an initial belief in terms of its content, was typically held in the form of a derived belief.
CONCLUSIONS A wider range of characteristics is required to define all the differences between delusion and the overvalued idea, and these have implications for belief modification programmes.