Daydreaming may contribute to the maintenance of grandiose delusions. Repeated, pleasant and vivid daydreams about the content of grandiose delusions may keep the ideas in mind, elaborate the details, and increase the degree of conviction in the delusion. Pleasant daydreams more generally could contribute to elevated mood, which may influence the delusion content.

We sought to develop a brief questionnaire, suitable for research and clinical practice, to assess daydreaming and test potential associations with grandiosity.

798 patients with psychosis (375 with grandiose delusions) and 4518 non-clinical adults (1788 with high grandiosity) were recruited. Participants completed a daydreaming item pool and measures of grandiosity, time spent thinking about the grandiose belief, and grandiose belief conviction. Factor analysis was used to derive the Qualities of Daydreaming Scale (QuOD) and associations were tested using pairwise correlations and structural equation modelling.

The questionnaire had three factors: realism, pleasantness, and frequency of daydreams. The measure was invariant across clinical and non-clinical groups. Internal consistency was good (alpha-ordinals: realism=0.86, pleasantness=0.93, frequency=0.82) as was test–retest reliability (intra-class coefficient=0.75). Daydreaming scores were higher in patients with grandiose delusions than in patients without grandiose delusions or in the non-clinical group. Daydreaming was significantly associated with grandiosity, time spent thinking about the grandiose delusion, and grandiose delusion conviction, explaining 19.1, 7.7 and 5.2% of the variance in the clinical group data, respectively. Similar associations were found in the non-clinical group.

The process of daydreaming may be one target in psychological interventions for grandiose delusions.