But the level of depression that Dr. Galambos, a psychologist, and her team found among girls in their late teens was quite unexpected.
The researchers used Statistics Canada's National Population Survey to monitor the mental health of 1,322 teenagers -- 648 boys and 674 girls -- between the ages of 12 and 19 over the course of four years.
They found that 25 per cent of girls between 16 and 19 experienced at least one major depressive episode within that four-year period.
"That was startling to me," Dr. Galambos said. "This is a substantial number of young Canadian women who should be identified as depressed and treated."
Depression was defined as experiencing several of a range of symptoms over a prolonged length of time, including fatigue, irritability, inability to make decisions, sleeping problems, a lack of interest in day-to-day activities and suicidal thoughts.
"It can be debilitating," Dr. Galambos said. "It could be the person who is lying in bed and can't get out of bed. It could mean crying every day for a few weeks."
As expected, the boys in the study were depressed only half as often as the girls and at some points, there were three times as many girls as boys who were depressed.
There is no real understanding of why there is such a difference between the sexes, she said.
"Some people will say well, maybe females are exposed to more stressful life events, or maybe they are more likely to react negatively to stressful life events.
"There's also some suggestion that there is a genetic link too, that there is some biological cause for girls becoming more depressed than boys do."
Other research has pointed to a link between smoking and depression so the team looked at that variable and found that the correlation is strong.
Both male and female teenagers who took up smoking during the course of the study were more likely to experience symptoms of depression over time, though not necessarily full-blown depressive episodes.
"And the reverse is also true,'' Dr. Galambos said. "If they smoked less over time, they were less depressed." Again, she said, nobody really understands why that relationship exists.
It could be that smoking causes depressive symptoms.
Or perhaps, Dr. Galambos said, the teens who are upset or disturbed or distressed earlier on "are feeling uncomfortable and are using smoking as a way to have an elevated mood."
Unfortunately, she said, "there may be longer-term negative consequences on depression from that earlier level of smoking."