When carrying out risk assessments, scientists may need to use default values at different stages of the evaluation process. Default values and assumptions can be of a methodological nature (e.g. rounding numbers) or used to take into account uncertainties for instance in extrapolating results of animal toxicity studies to human populations. EFSA’s Scientific Committee has published guidance for harmonised default values to be used in EFSA’s risk assessments when insufficient or no actual measured data exist.
Default values used in risk assessments should always be scientifically justified and be based on existing data representing average (typical) values for the missing information. The guidance focuses on the most commonly used default values by EFSA’s Scientific Panels, Scientific Committee and Units. It identifies harmonised default values for body weight, total liquid intake, a number of uncertainty factors used in establishing health-based guidance values, and factors for converting chemical substance concentrations in feed or drinking water to doses utilised in experimental animal studies to assess toxicity of the substances.
Among its recommendations, the Scientific Committee proposes default values for EU population body weight to be used in the absence of empirical data. The values - 70 kg for adults, 12 kg for toddlers and 5 kg for infants - are based on a review of detailed information available in EFSA’s Comprehensive Food Consumption database. For health-based guidance values such as Acceptable Daily Intakes an average body weight of 60 kg for worldwide adult populations has so far been commonly used. Based on actual EU data, the Scientific Committee considers that 70 kg is a more realistic estimate of the current, average body weight of EU adults.
The Scientific Committee highlights that whenever actual data are available, these should be used instead of the default values. For example, when assessing the possible adverse health effects of a chemical substance for a specific sub-population (e.g. women of child bearing age), actual body weight data for this population should be used in the exposure assessment. Therefore, EFSA’s Scientific Panels, Scientific Committee and Units may use alternative values in their assessments if scientifically justified.