The full paper[1] addresses this to some extent (my emphasis added below): "Accurate estimates of the lifetime history (prevalence) of traumatic brain injury w

The full paper[1] addresses this to some extent (my emphasis added below): "Accurate estimates of the lifetime history (prevalence) of traumatic brain injury within the general population are scarce, which makes it difficult to compare rates of injury among homeless people with rates among those in the community. Two community cohort studies suggested prevalence rates of 3.8% (for experiencing at least 1 admission to hospital for traumatic brain injury by age 35; northern Finland birth cohort) and 31.6% (for experiencing a traumatic brain injury for which the person received medical care; Christchurch, New Zealand, birth cohort). Together, these data suggest that rates may be higher among people who are homeless than within the general community. A recent study estimated that homeless men had rates of head injury 14 times higher than rates for the general population of Canada, with a rate 400 times higher among those who were chronically homeless and had drinking problems." And not oranges and oranges comparison, but[2]: "Separately, a recent study by Dr. Stephen Hwang of the hospital's Centre for Research on Inner City Health, found the number of people who are homeless or vulnerably housed and who have also suffered a TBI may be as high as 61 per cent -- seven times higher than the general population." [1] http://www.cmajopen.ca/content/2/2/E69.full http://www.cmajopen.ca/content/2/2/E69.full [2] http://www.ncbi.nlm.nih.gov/pubmed/24651000 http://www.ncbi.nlm.nih.gov/pubmed/24651000