First-born children are more likely to have allergies, and conditions including autism, attention deficit hyperactivity disorder ( ADHD), Tourette's, and obsessive-compulsive disorder (OCD), the study found. "These ideas have generated a rich but fragmented empirical literature, with individual studies examining birth order in relation to specific diseases or developmental outcomes." For completeness, comparisons were run between siblings in the same family, and first-born and second-born children from different families. Of the 569 diseases analyzed, 150 showed different associations for first-born and second-born children, including those mentioned above. There have been a host of interesting studies on the impact of birth order amongst children.