Associations between IQ and common mental disorders: the 2000 British National Survey of Psychiatric Morbidity.

ABSTRACT

BACKGROUND: Associations have been described between lower IQ and serious mental illness. Associations between common mental disorders (CMDs) and IQ have received little research. The objective of this study was to investigate the association between verbal IQ and CMD symptoms and diagnoses, and to investigate the role of potential mediating and confounding factors. METHOD: Data were analysed from a British national survey with an analysed sample of 8054 people aged 16-74 years. Associations between verbal IQ (NART) and mental symptoms/disorders (CIS-R) were analysed with covariates including education, social class, income, debt, problem drinking, life events, physical health and relationship quality. RESULTS: CMD was associated with lower IQ. This association was stronger for depressive disorder/symptoms than for generalised anxiety disorder/symptoms. The most important covariates were education, social class, income and relationship quality. CONCLUSION: The association between lower IQ and CMD is partly accounted for by adverse social/socioeconomic conditions. Stronger associations for depression than anxiety may indicate an effect of IQ on the way mental distress is communicated.