Apparently the new version of "epidemiology" allows looking at total numbers of fatalities with and without helmets, and without any data on the percentage of motorcyclists who wear helmets when riding, or the nature and extent of the injuries suffered by the victims of the fatal events can determine the prophylactic power of helmets from the limited data at hand.

The same epidemiologist can use the same analysis method to gaze at the NHSTA data set to determine the prophylactic power of reducing engine size of motorcycles again without knowing anything about percentages of riders who ride bikes with big engines.

More importantly such "analysis" ignores all other variables at play including that riders of big bikes or riders without helmets may ride differently than riders who ride ride small bikes or wear helmets.