Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
household visits and interviews may not be kept as the field personnel
expect.
A good approach for identifying problems and alternatives is the
use of pilot studies before full implementations of the field
component of a study. In pilot studies, trained staff perform the
complete set of SOPs established for the full investigation on a small
subset of the sample population. Thus, pilot studies also have the
purpose of effectively providing final training of all field
personnel. The information collected during these studies is very
useful for adjusting the study plan and SOPs for local conditions. It
is important that all personnel participating in a field study, i.e.,
study design personnel, principal and co-investigators, laboratory
staff and field personnel require practical experience with the local
field conditions. Pilot studies provide the means to obtain such
experience.
Another potential confounder in population studies is the
Hawthorne effect; that is, the alteration of behaviour patterns that
might affect exposures as a result of participation in the study. For
example, many population-based field studies provide compensation to
individuals who agree to participate. Monetary compensation could
alter behaviour patterns that may affect exposure: for example, the
participant may decide not to go to work (a typical activity) the day
he receives the payment and instead spend the time performing an
activity that is not customary. This problem can be resolved by
offering the payment a short time after the participants have
completed the monitoring period. The presence of an environmental
monitor (e.g., an air sampling inlet and pump) may cause participants
to avoid situations in which they may feel conspicuous, such as their
place of employment. An innovative approach for assessing the
influence of this effect is to expand the study to include a subsample
of participants who engage in only a portion of the study (e.g., a
time-activity questionnaire) and to compare the results for this group
to those for the remainder of the population that completed the full
monitoring programme.
11.7 Summary
QA includes independent study monitoring that assures laboratory
management and users of data that facilities, equipment, personnel,
methods, practices, records and controls confirm to accepted quality
management principles. Errors in exposure data may be due to
analytical variation as well as changes that may take place during
sample collection and handling, preparation and storage of samples,
and data keeping and data recording. Analytical variation can be
divided into two major categories: accuracy, which refers to the
agreement between the amount of analyte measured and the amount
actually present, and precision, which refers to the random
variability or reproducibility of the method.
The study plan is the most important document for providing
information on the critical components of an investigation, e.g.,
responsible personnel, sample collection, sample storage and
pre-analytical treatment, analytical procedures and data analysis.
SOPs are appended to the study plan and contain written detailed
instructions on how to perform certain routine field and laboratory
activities. The study plan and SOPs can be seen as management
directives designed to ensure that all personnel associated with study
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