EXCLUSIVE

The cost of mental illness to Australia's collective wellbeing has reached $190 billion a year - equivalent to about 12 per cent of the economy's annual output.

The Herald-Lateral Economics Index of Australia's Wellbeing - which uses a range of indicators to measure changes in national welfare - calculates a dollar figure for how mental illness affects the Australian population beyond its narrow economic effect.

It shows that the wellbeing cost of mental illness in the March quarter alone was $48 billion. Official economic figures only pick up the direct economic effects of mental illness, such as work absenteeism. But mentally ill people tend to report lower levels of wellbeing, on average, and the Herald-Lateral Economics index puts a dollar figure on these non-economic - but very significant - effects.

Index author Nicholas Gruen said the results drew attention to how much mental illness is affecting Australia's collective wellbeing.

''These big numbers put in perspective the real cost of mental illnesses to the community,'' Dr Gruen said.

But there was some good news. The drag on wellbeing due to mental illness has been offset to some extent by an increase in the rate of treatment for mental illness over the past four years.

''The rate of treatment of mental illness seems to be increasing strongly,'' the index report said. ''The proportion of the mentally ill with GP treatment plans has risen to 19.9 per cent from 16.8 per cent in 2009.''

The wellbeing index calculates that each 1 percentage point increase in the rate of treatment adds $1 billion a year to our collective wellbeing.

Even so, the annual wellbeing cost of mental illness is now $28 billion a year more than it was in 2005-06. It is estimated about one in five Australians suffers from a mental illness.

The index highlights how obesity is also a major drag on national wellbeing and calculates its wellbeing cost to be more than $120 billion a year.

The index report says obesity has been increasing faster than other index components ''so the relative importance of obesity in wellbeing is rising''.

Despite the negative effects of mental illness and obesity, Australia's overall wellbeing grew much faster than gross domestic product last year. The Herald-Lateral Economics wellbeing index rose by 3 per cent in the March quarter to be up 5.5 per cent for the year. Gross domestic product figures released by the Bureau of Statistics on Wednesday revealed growth of 0.6 per cent in the quarter and 2.5 per cent for the year.

The main factor driving national wellbeing higher was a 12.7 per cent increase in the rate of Australia's human capital accumulation - our collective skills - in the year.

The increase in adult education has been an important driver of recent improvements in the wellbeing index. When added to population growth, this trend means Australia has a better trained workforce as well as a larger one.

''This investment in the skills and know-how of the population should ensure that the Australian population is able to generate significant income in the future, even if the prices of our resources decline,'' the report said.

Australia's national income - another important component of the index - rose a modest 0.9 per cent.