Research co-authored by a professor of psychology and gender and women's studies at the University of Wisconsin-Madison has discovered that gender differences in individuals who suffer from depression can be found in those as young as 12 years old. The results confirmed that the psychological condition largely affects females.

The study was published in the journal "Psychological Bulletin." The analysis was based on existing studies that examined over 3.5 million people in more than 90 countries.

In a post on UW Madison's official website, the study is expected to convince doubters that more women are affected by depression than men. That's not to say that the condition should be stereotyped as a women's disorder since a third of those affected are men.

The gender gap was already present in the earliest data examined by co-authors Hyde, Rachel Salk, now a postdoctoral fellow in psychiatry at the University of Pittsburgh School of Medicine, and Lyn Abramson, a professor of psychology at UW-Madison. Hyde said that the gap was already present at age 12. This is a lot earlier than what previous studies have discovered.

It was added that the gender differences were less obvious after adolescence. This has never been identified but the rate of individuals with depression is still close to twice as high for women.

The researchers believed that puberty could explain the onset of depression in 12 year old girls. In this stage of life, girls experience hormonal changes and changes in the social environment as well.

The team also checked the relationship between depression and gender equity in income. Nations with greater gender equity had larger gender differences. This meant that more women were diagnosed with major depression.

This is actually opposite of what the researchers expected. They hypothesized that this occurred because women have more contact with men in gender-equitable nations, who do not show feelings of depression since it does not fit with the masculine role.