A derivation then validation study was done on over 40000 children with head injuries to identify factors associated with clinically important brain injury. Prediction rules based on history and examination findings were developed for children younger than two years and for children two years and older. Both rules had high negative predictive values and may be useful tools in supporting the decision not perform a head CT.
Identification of children at very low risk of clinically-important brain injuries after head trauma: a prospective cohort study
Lancet. 2009 Oct 3;374(9696):1160-70