Delusions and hallucinations are common among healthy individuals but may differ from the symptoms experienced by persons with schizophrenia. It is hypothesized that specific dimensions of delusions, such as the distress associated with them, preoccupation, conviction or their content might be more relevant in distinguishing persons with from persons without schizophrenia than the mere presence of delusional beliefs. Second, it is investigated whether delusional beliefs are as closely linked to hallucinations in a non-clinical population as in persons with schizophrenia. The Peters et al. Delusions Inventory and the Launay Slade Hallucination Scale — Revised were used to assess delusional ideation and hallucinatory experiences in a population sample that reflects the general population in age, education and gender (n = 359) and in persons diagnosed with life-time schizophrenia in varying stages of remission (n = 53). There was a strong association of delusional ideation and hallucinatory experiences in both groups. Stepwise discriminant function revealed the distress associated with delusions as well as beliefs involving persecution and loss of control to be the most relevant aspects in distinguishing persons with from persons without schizophrenia. It is concluded that delusions should be assessed multi-dimensionally, laying particular emphasis on distress and content of beliefs.
Delusions are defined in the DSM-IV™ Guidebook as fixed, false beliefs that are not widely held in the context of the individual's cultural or religious group, are impervious to compelling evidence of their implausibility and are held with total conviction (Frances et al., 2005). The classic distinction between presence and absence of delusions is categorical, differentiating between presence and absence of severe mental disorder and arguing that there is a distinct mechanism for the formation and fixation of delusions in contrast to normal or overvalued ideas (Jaspers, 1946). The categorical classification has been criticized for several reasons: First, it has been acknowledged that delusions involve other aspects than the mere presence of an odd belief. These include distress associated with the belief, the preoccupation with it and the level of conviction (e.g. Appelbaum et al., 1999 and Peters et al., 1999b). Second, in spite of having been defined as fixed, delusions are not unchangeable (Appelbaum et al., 2004, Sharp et al., 1996 and Kuipers et al., 1997). Third, the high co-morbidity of schizophrenia with other DSM-IV diagnoses (Sirius, 1991, Fenton, 2001 and Hanssen et al., 2003) suggests the presence of common pathologies (Widinger and Samuel, 2005). Finally, multiple findings indicate that delusions and hallucinations are commonplace in healthy populations, with prevalences up to approximately 25% depending on the definitional criteria (Gallup and Newport, 1991, Eaton et al., 1991, Peters et al., 2004, Peters et al., 1999b, Freeman et al., 2005 and Tien, 1991). This provides support for continuum models of psychotic symptoms (Strauss, 1969, Claridge, 1987, Johns and van Os, 2001 and McGovern and Turkington, 2001), which postulate that schizophrenia is not a discrete illness entity, but that psychotic symptoms differ in quantitative ways from normal experiences and behaviors.
Compared with participants from the general population, participants with schizophrenia endorsed significantly more items, experienced more total distress about beliefs, spent more time thinking about them and had higher values for total conviction. In Table 2 means and standard deviations of the PDI scales and results of the significance tests are depicted. In- and outpatients did not differ significantly on the number of endorsed beliefs (inpatients = 13.1, SD = 7.3; outpatients 15.0, SD = 8.9), mean distress (inpatients = 2.2, SD = 1.1; outpatients = 1.9, SD = 1.0), preoccupation (inpatients = 1.8, SD = 1.1; outpatients = 1.8, SD = 1.1) and conviction (inpatients = 2.4, SD = 1.3; outpatients = 2.3, SD = 1.2) or the LSHS (inpatients = 15.6, SD = 11.2; outpatients = 17.9, SD = 12.1).
