This study was based on information gathered from over 21,000 children living in the United States, as well as from their parents and teachers.
هذه الدراسة مؤسسة على معلومات جُمعت من اكثر من ٠٠٠‏,٢١ ولد يعيشون في الولايات المتحدة ،‏ اضافة الى والديهم وأساتذتهم .‏