Mild traumatic brain injury (mTBI) is associated with various neurological and cognitive problems, but causality is often less clear. For example, postconcussion syndrome (PCS) was widely assumed to be a consequence of neural damage until it was demonstrated that: (1) the symptoms of PCS are not specific to brain injury, being common in the general population,1 (2) ‘PCS’ is as common in those who experience physical trauma without brain injury as those who experience mTBI,2 (3) preinjury factors, such as a history of anxiety or affective disorder, predict development of PCS,2 (4) PCS has a strong relationship with PTSD-type symptoms3 and (5) lower cognitive function may be a risk factor for mTBI rather than a consequence of it.4

Vaaramo et al⁵ underline the problems inherent in assuming causation on the basis of association in head …