When asked to describe a typical child with attention deficit hyperactivity disorder (ADHD), most people would describe a young boy who climbs on things, is impatient and does not do what he is told. Few people would describe a bubbly young girl with lots of friends, who works hard to get good grades.

It may be, however, that the girl does experience ADHD symptoms that interfere with her daily life — and that these symptoms are overlooked by the adults around her.

Undiagnosed ADHD has long-term consequences including an increased likelihood of engaging in risky behaviours — such as unprotected sex and substance use — as well as academic underachievement and low self-esteem. Perhaps most alarmingly, girls who struggle with ADHD for a long period of time can suffer from mental health problems.

As a psychologist in clinical practice, I used to see many older girls and adult women with ADHD who had already been prescribed medication to treat anxiety and depression. Early diagnosis then is vital.

Assessment scales use data from boys

Individuals with ADHD exhibit three main clusters of symptoms: hyperactivity, impulsivity and inattention. Although three times as many boys are diagnosed with ADHD in childhood than girls, the diagnostic rates in adults are more equally divided between males and females. This suggests girls go unnoticed when they are younger.

As a disorder traditionally seen as affecting males, and with males referred more often for a diagnosis, research to assess ADHD has been based on samples largely consisting of boys. It has been argued that the rating scales developed to assess ADHD have been based on the behaviours observed in the mainly male research samples.

ADHD can look different in girls than boys. A boy who is hyperactive might have trouble sitting in his seat in the classroom — so he sits with one knee on the seat and one foot on the floor. It is likely, given his constant shifting and unequal balance on the seat, that the back legs of the chair will eventually lift up and the chair pitch forward causing the boy to fall to the floor.

In contrast, a hyperactive girl may be out of her seat but have taken on the role of classroom helper, wandering around to different desks. A teacher completing a rating scale might rate the boy higher on hyperactive questions than the girl because the second example is not seen as disruptive. Thus, girls do not score as high as boys on these scales and are underrepresented because they do not meet criteria for a diagnosis.