Researchers have identified head circumference and head tilting reflex as two reliable biomarkers in the identification of autism spectrum disorders (ASD) in children that are between 9 and 12 months of age. ASD is identifiable as early as two years old, although most children are not identified until after the age of four. While a number of studies have reported that parents of children with ASD notice developmental problems in children before their first birthday, there has yet to be a screening tool to identify those children.