Mental illness can be a big financial cost both to individuals with mental-health problems and society as a whole. Most studies into the effects of mental illness on wages have been done in higher-income countries but mental illness is a problem all over the world and the World Health Organization surveyed 44,561 people in 19 different countries about their mental health and their earnings. The respondents were in countries all over the world with widely different incomes. The study found that, on average, respondents with serious mental illness earned on average a third less than median earnings.
Levinson, Daphna ... [et al] - Associations of serious mental illness with earnings: results from the WHO World Mental Health surveys British Journal of Psychiatry August 2010, 197(2), 114-121