HEAD OR NECK INJURY INCREASES THE RISK OF CHRONIC DAILY HEADACHE: A POPULATION-BASED STUDY

Abstract

In a case-control study, it is difficult to ascertain whether the headache started or worsened after the trauma. It is also generally acknowledged that self-reported exposure in case-control studies may be subject to differential information bias. For example, an unfortunate outcome like chronic headache will serve as a stimulus for the patient to scrutinize the past and increase the likelihood to recall certain events. This is briefly mentioned in the Discussion, but the true importance of this problem is not acknowledged, since it is stated that “Recall bias may lead to over- or under-reporting of head injury in CDH cases and controls.”¹