TB results the frequency of latent TB in the total cohort was 3% (5/155), whereas the TB transmission rate in the actual TB exposure study was estimated to be 2% (3/155).
Assessment of risk from exposure to multiple agents can be derived either from epidemiological studies in relation to actual exposure or from laboratory studies after controlled exposure to different agents.
However, the actual exposure status of individual study participants was not known at the time the symptom data were collected but was established only after the air and water analyses had been completed, making it less likely that study participants could influence study results.
In exposure terms, both differential and nondifferential misclassification can occur, for example, when environmental measures do not accurately reflect actual exposure, and may lead to biased study results and/or a reduction in study power.
Even so, aassessment of jobs and exposures obtained through interview should be critically evaluated, as the likelihood of exposure misclassification is higher than for studies with actual exposure measurements.
Many of the TCE studies lack actual exposure measurements for individual subjects, and surrogates such as available current or historical monitoring data are often used to reconstruct exposure parameters.
"Since this is a cancer-register-based study, we don't have actual exposure information on the subjects we evaluated," said Dr. Margaret A. Tucker, the study's lead author and director of the institute's human genetics program.
A recent study suggested PVT reflected actual exposure of children to non-core food advertising (23).
Conversely, whilst drugs and their metabolites can be detected in the environment and their concentrations measured or predicted, apart from a limited number of studies [ 40, 41], actual exposure in wildlife is generally not known.
All methods of estimating individual exposure to air pollutants will misclassify individual exposure to a degree, because measuring actual exposure is impractical, especially in large scale studies.
