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Table 1 Possible sources and examples for each error type

From: Methods to account for uncertainties in exposure assessment in studies of environmental exposures

Error Types Possible Sources Examples
Variability Differences in individual’s location, exposure or behavior, randomness, etc. Individual-specific exposure estimates differ with distances from the pollutant source [12]; Exposure to pesticides or bacteria may vary by season [12]; Different patterns of food intake may result in different exposures across individuals [12].
Uncertainty Lack of knowledge in specifying exposure pathways, simplified model assumptions, failure to account for possible correlations between variables, etc. There is uncertainty in the level of exposure to insecticide sprays due to the unknown exposure pathway (inhalation, dermal contamination or both) [61]; There is uncertainty when calculating one’s inhalation rate because of the failure to account for the dependency of body weight and breathing volume [61]; There is uncertainty in the estimated room air concentration because of the unknown release rate of the chemical. [61].
Shared Error Incomplete knowledge about the parameters that affect the exposure measurements of group. Inaccurate estimations of the ground deposition of certain contaminants may affect the estimation of exposure for all people who live in the same area [18]; Errors from an uncertain of a biased measuring device when it is used to a group of people [54].
Unshared Error Lack of knowledge about the parameters that vary randomly between subjects. See the examples for classical error, Berkson error and unshared non-random error.
Classical Error Imprecise measuring device, repeated measurements that vary around the true value, etc. Using the replicated urinary nitrogen as a measured biomarker to investigate the true long-term dietary protein intake, etc. [3, 44]
Berkson Error The same exposure value is assigned to a group with similar characteristics. Air quality records collected by a monitoring station are assigned to all subjects in the study as estimates of true individual exposure to pollutants [62]; When job-exposure-matrix is used to estimate the individual exposure in occupational epidemiological studies, same exposure estimate is assigned to the groups of people with same occupation code [17, 63].
Unshared Non-random Error Imprecise knowledge in individual specific parameters. Errors in personal residence history records [7]; Errors in personal consumption rates of contaminated foods [7].