Now a study of nearly 400,000 children between four and 17 years old in Taiwan has shown that the percentage of youngsters diagnosed with ADHD significantly changes depending on month of birth. Where just 2.8 per cent of boys born in September have the condition, the figure jumps to 4.5 per cent in August, rising steadily over the school year. For girls it rose from 0.7 to 1.2 per cent.