Factors associated with delusional themes

There is debate regarding the definition and development of psychiatric delusions, but they are typically defined as false, idiosyncratic beliefs. The extent to which delusional themes differ across the world and according to demographic factors is unclear. The first section of this thesis includes a meta-analytic review of the prevalence of five common delusional themes (persecutory, reference, grandiose, control, and religious) across the world, including sub-group and meta-regression analyses. There were 117 studies (130 samples) included in the systematic review and 109 samples were meta-analysed with a total of 17,922 participants. Persecutory delusions were most common delusional theme, followed by reference, grandiose, control, then religious delusions. Prevalence rates of delusions did not significantly differ between developed and developing countries or according to study quality or year of publication. Persecutory and religious delusions were more prevalent in younger samples, and grandiose, control, and religious delusions were more prevalent in males. As predicted, persecutory delusions are the most common delusion across the world. The prevalence of delusional themes did not differ between developed and developing countries, but they were influenced by age and gender, suggesting that delusions reflect universal human concerns that vary according to stages of life and gender. Prevalence rates of delusional themes may differ according to other cultural factors, such as the level of individualism and income inequality. Grandiose delusions have received relatively little empirical investigation and the second section includes two empirical studies on grandiosity in the general population. Based on past research on predictors of paranoia and other strongly held beliefs, the first study was a cross-sectional survey investigating factors associated with grandiosity. Younger age, male gender, non-white ethnicity, paranoia, religiosity, and narcissism were associated with grandiosity. Paranoia was associated with grandiosity, attachment anxiety, negative self-esteem, and younger age. Grandiose delusions have been described as providing a sense of meaning in life and Terror Management Theory proposes that human's boost their selfesteem to protect against existential anxiety. Therefore, the second study aimed to test whether grandiosity reflects a defence against existential anxiety. An online between-subjects experiment investigated changes in participant's grandiosity and self-esteem after being primed to think about their mortality or dental pain, as a control condition. There was no effect of mortality salience on changes in self-esteem or grandiosity, as self-esteem significantly increased, and grandiosity significantly decreased in both conditions. Interestingly, males and non-white participant's grandiosity decreased in the dental pain group, but not in the mortality salience group, whereas female and white participant's grandiosity decreased in both conditions. Taken together, the findings suggest that male gender, non-white ethnicity, high religiosity, narcissism, and paranoia are associated with increased grandiosity. Future research is needed to replicate these findings in clinical populations with more diverse samples and include different subtypes of grandiose beliefs.