The study includes 126,734 dementia cases in the analysis; 6,374 had experienced TBI. A potentially powerful study.
The data clearly shows an increased risk of dementia diagnosis within the 2 years following TBI. However, there is no variation in risk between 4 and 14 years after TBI, suggesting a completely uniform acceleration, which would be hard to explain. There is also decreasing risk as age increases, yet older people are more vulnerable to dementia. This also is hard to explain.
The authors call for more to be done to prevent TBI. Dementia is a growing problem.
Motor and sports insurers would be especially sensitive to this issue if it turned out that TBI was a legal cause of dementia. Especially if this was young onset dementia.
Although not assessed by the authors, a large proportion of the observed association is probably due to reverse causation. Around 67% is probably due to reverse causation, but only the authors can quantify this precisely. An unknown proportion is due to residual confounding e.g. from educational attainment. There are good reasons to suspect residual confounding.
A full report is included in the next issue of the Radar journal.
It is to be hoped that Fann et al. will be encouraged to estimate the contribution made by reverse causation and to estimate the scale of the systematic error arising from probable confounders.