Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
for temporal completeness and clarity of responses. Ideally, this
should be done in the presence of the participant, and within 24 h of
completion of the monitoring period. Another quality assurance step
involves the use of a uniform system to code information on individual
activities into microenvironmental categories.
The validity and reliability of the diary data may be increased
by the use of study forms that are simple and easy to understand. The
language of the questions and instructions must be simple and the
method of selection of answers, or of filling in data, obvious to
minimize coding errors. The number of items on the questionnaire
should be kept to a necessary minimum. Only the information for which
there is clear use in analysis and data interpretation and which
serves directly the study objectives should be included in the diary
form.
Verifying the validity of time-activity data is extremely
difficult, if not impossible, because an absolute standard does not
exist. Several researchers have sought to assess the reliability of
self-reported data through test-retest procedures and by comparing
different methods of collecting the same type of information (Laporte
et al., 1985). The University of California at Berkeley ozone study
required college students to recall time spent in physical activities
outdoors, over years. The information was used as a surrogate to
improve long-term ozone exposure assignment in an epidemiological
study (Künzli et al., 1997b). The test-retest study revealed rather
high correlations for time spent in heavy ( r = 0.81) or moderate
( r = 0.61) activity (Künzli et al., 1997b). This level of
concordance is similar to that observed in dietary intake validation
studies where food-frequency questionnaires and diet records
correlated in the order of r = 0.6 for the intake of a variety of
nutrients (Rimm et al., 1992). Robinson (1985) found that a variety of
methods for collecting time-activity data, including 24-h recall
surveys, same-day diaries, records of the activities during 40
randomly selected moments throughout the day (signalled using a
beeper), and recall of the activities during a randomly chosen hour
yielded essentially similar sample distributions of time the sample
spent in a variety of activities. Quackenboss et al. (1986) also found
consistency between diaries and the responses to self-administered
recall questionnaires. Juster (1985b) found reasonably strong
agreement in the reports of spouses regarding whether their partner
was present at any given time throughout the day. Other comparisons of
methods show that when asked about the usual time spent in selected
activities, respondents tend to over-report time in unscheduled
activities (relative to that recorded on their diaries), but reports
are consistent for habitual activities such as commuting to work
(Robinson, 1985). Waldman et al. (1991b) showed similar results when
comparing activities recorded in electronic diaries with next-day
recall; concordance between the methods was highest for routine,
long-duration activities. Additional research, however, is necessary
to determine the extent and direction of bias for the activities and
the time frames of most concern in an exposure context (e.g., the
frequency with which a person uses household cleaning products rather
than the total time spent cleaning).
5.3.3 Inter- and intra-person variability
To be of use in exposure assessment, time-activity data must
describe the aspects of human behaviour that influence the variability
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