In this issue, Leland et al1 calculate an injury rate for children in day-care centers that is expressed as the number of injuries per "child day." Computation of such incidence rates helps determine the relative importance of different settings and activities in the occurrence of injury. Rates are also important for evaluating the effect of control measures. However, choosing appropriate numerators and denominators for calculating rates can be difficult.
What constitutes an injury worthy of counting, ie, what belongs in the numerator? Leland et al1 count all injuries, no matter how trivial, as long as they were recorded in a logbook and involved physical or emotional distress. For some purposes, this definition may be useful; however, for public health and epidemiologic purposes, it may be less useful. The reasons are twofold. First, minor injuries, like bumps and scrapes, are difficult to define consistently. Such injuries may be more
SACKS JJ. In Rates We Trust. Am J Dis Child. 1993;147(8):813. doi:10.1001/archpedi.1993.02160320015004