The underlying philosophy of science is that of determinism and in the quantitative sciences ‘causal’ determinism can be empirically tested.1 Whether investigating the effects of Helicobacter pylori bacteria on the prevalence of peptic ulcers2 or elements of road infrastructure on the risk of a cyclist injury,3 the empirical approach whereby observations are undertaken to answer established hypotheses is fundamental in science. It seems ironic, therefore, that Michael Kary's commentary4 totally dismisses the value of causal determinism; a fundamental tenet of epidemiology.

It is unfortunate that Kary chooses to not consider the historical epidemiological literature that readily highlights the role that epidemiology has played in injury prevention and specifically, road injury prevention. Luminaries such as William Haddon5 and John Gordon,6 both public health physicians, applied evidence-based medicine (EBM) (at the time it was not referred to as EBM) to disentangle much of the dogma in injury prevention. Kary, in his commentary, suggests that epidemiology dismisses mechanism-based reasoning and yet it was colleagues such as William Haddon who began applying what is coined in road safety research today, a systems approach to safety. Haddon embraced mechanism-based reasoning by including elements of the environment (both the physical and social environments), the host (the driver, cyclist or other road user) and the agent (the energy exchange generated by the motor vehicle and all its variants) in crash causation.

In Kary's commentary, he highlights a number of limitations of recently published cycling studies that have applied epidemiological approaches.7–9 At first his concerns appear legitimate; …