Two criteria that have been used in comparing decompression schedules:Safetyare efficiency and efficiencysafety, where [[decompression efficiency]] is defined as the ability of a schedule to provide acceptable safety from decompression sickness in the shortest time spent decompressing, and decompression safety, or converely, risk, is measured by the probability of decompression sickness incurred by following a given schedule for a given dive profile. Since it is impracticable to eliminate all risk using current knowledge of the effects of several variables, risk is derived by statistical analysis of the outcomes of exposure and decompression profiles, and an acceptable risk is stipulated, which may vary depending on the circumstances of the application.<ref name="Edel 1980" />
