Attention-deficit hyperactivity disorder — more commonly known as ADHD — affects those in the US far more than any other country.

The gulf between the US and the rest of the world is only expected to increase in coming years, according to GlobalData research.

In 2014, 6.91 percent of those over the age of three in the US were found to have ADHD, while the five largest European countries combined 1.23 per cent were diagnosed with the condition and 1.21 percent in Japan.

It is difficult to determine why ADHD prevalence in the US is so much higher.

The difference has been attributed to differences in the studies’ methodology, diagnostic criteria, and case identification. Others believe ADHD is over-diagnosed in the US, or at least there is a perception of over-diagnosis due to over medication, dramatic media coverage, and anecdotal personal experiences.

Social acceptance of mental illness may contribute to the higher prevalence of ADHD in the US.

Meanwhile in some countries, such as Japan, negative perceptions of mental illnesses are roadblocks to disease awareness and diagnosis.