Source: https://www.amazon.com/Parenting-Strong-Willed-Child-Clinically-Six-Year-Olds/dp/0071667822/ref=as_li_ss_tl?ie=UTF8&qid=1481300388&sr=8-1&keywords=Parenting+the+Strong-Willed+Child&linkCode=sl1&tag=nhm00-20&linkId=3ad168f419f98543351e888f419756b9