• Public health
• theory
• drowning
• epidemiology
• risk factor research

Mitchell, Williamson and Olivier's1 study estimated drowning rates for the Australian state of New South Wales (NSW) in 2005 based on resident population person-time exposure to swimming. The authors state (p. 261) that ‘failure to adjust injury rates for exposure to a hazard necessarily results in poor estimates of risk’ and, based on their findings, conclude (p. 264) drowning mortality rates to be ‘more than 200 times higher than equivalent exposure-adjusted rates for road traffic fatalities.’ This fact is cited in the Royal Life Saving Society's 2010 National Drowning Report2 (p. 3).

However, comparison data detailed below suggest that the reported time exposure drowning rate presents a gross overestimation of swimming risk. This is due to deficiencies in reported numerator data and denominator estimates.

The majority of unintentional drowning death cases included in the reported numerator would be unlikely to come from the population denominator (swimmers). This is a key principle for calculating population rates.3 Australia-wide unintentional drowning deaths reported for July 2004 to June 2005 identified 97 …