Phase of investigation
During the selection process of our review for risk or protective factors of the course of “headache“, a common recurrent pain condition, we did not put any restriction on phase of investigation. We did this because, in the child pain prognosis literature, studies are rarely grounded in theoretical frameworks so there are rarely any phase 3 explanatory study published  and phase 2 exploratory studies are not very common. Therefore, our review majorly includes phase 1 exploratory studies that identify potential prognostic factors which are particularly vulnerable to type I errors (false positive results). Consequently, the quality of evidence from the studies selected in our review could not be initially rated high.