The Bergen-Montpellier grandiose ideas questionnaire – B-MGI: a new tool for measuring grandiose delusions

ABSTRACT Introduction: Grandiose delusions (GD) are frequent in some clinical populations and can also be found in a minority of the general population. Despite the high prevalence, no specific tools have been developed to assess GD extensively. The present study aimed to develop and validate a specific questionnaire: the Bergen-Montpellier grandiose ideas questionnaire (B-MGI). Method: To begin with, an over-inclusive item pool was generated and subjected to exploratory factor analysis to identify the items to keep and to discard. This was done using a large sample of 183 participants from the general population. A second sample of 181 healthy participants was then used to confirm the 4-factor structure of the B-MGI. Results: Significant, albeit weak, correlations were found between the B-MGI and positive psychotic symptoms, providing initial support for convergent validity. Moreover, the B-MGI was poorly related to negative psychotic symptoms, supporting the discriminant validity of the B-MGI. Conclusion: The B-MGI is the first self-report measure that targets specifically GD. The questionnaire demonstrated good preliminary psychometric properties. Future studies should explore further the psychometric properties of the B-MGI.