She emphasises, however, that depression is a major cause of disability and leads to feelings of sadness and hopelessness that can last for months or years.
Unlike previous research, her study links depression to suicide and heart disease statistics.
"Depression is a big problem," Ferrari says.
"Although there are efforts to build awareness, there is still a lot of work that needs to be done in Australia and overseas.
"The bottom line is that depression is very important chronic disease that starts in young people and affects people for most of their adult life."
The study, published in the journal PLOS ONE, is important from a public health point of view, says Professor Nick Glozier from the University of Sydney.
The more common something is the more disabling it is, he says.
"This helps planners prioritise where money is spent."
He says, however, that the study shows shows Australia is a healthy nation overall.
"We spend a lot of time speaking about how badly Australia is doing in terms of its health. But it is actually a pretty healthy population.
"The fact that we have a peaceful society is really helpful."
In stable countries there does not seem to have been any change over the past 20 years in the proportion of people who are depressed, he says.
"We spend phenomenal amounts of money on very rare and difficult-to-treat diseases compared with the amount of health service dollar spent on the second most disabling condition in the country.
"The study confirms we need to pay attention to depression.
"It's really, really important from a public health point of view."
- AAP
