An aura of mystery surrounds the concept of ADHD. Some scientists think it’s like a unicorn — everyone knows what it is, but nobody has ever seen one. Other scientists argue that ADHD existed even before the authors of the DSM-IV invented the words for it in 1994.

The articles ADHD Does Not Exist, Part 1 and Part 2 discuss the question of whether or not it’s a single illness, or just a collection of different symptoms and problems. A major factor in this argument is its origins; some say it is caused by early onset stress in childhood, while others suggest it is genetic and children are born with it.