Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
Similarly, information about an individual's health condition may
be important in characterizing their time-activity pattern. For
instance, the limited data available on asthmatics suggests they may
spend more time indoors than the general population (Goldstein et al.,
1986, 1988; Lichtenstein et al., 1989; Schwab et al., 1991). As
asthmatics are particularly sensitive to air pollutants, this activity
information is important.
Socioeconomic status may influence time-activity patterns related
to, for instance, time spent travelling to work or outdoors.
Currently, however, the gap existing in time-activity databases with
respect to the activity patterns of sensitive (e.g., elderly) and
potentially high-risk (e.g., low socioeconomic status) subgroups, is a
limitation for extension of exposure models to these groups. Further
study is needed to determine the extent to which income, education and
occupation are reliable surrogates for exposure-related factors (e.g.,
housing unit size and condition).
5.2.3 Data collection methods
Sociologists pioneered studies of activity patterns (Szalai,
1972; Chapin, 1974; Robinson, 1977). These "time budget"
investigations, which have been conducted in several nations,
emphasize the purpose of activities (cooking, eating, TV watching).
Ott (1989) summarizes such studies in relation to their usefulness to
exposure assessment; a basic drawback for exposure assessment
applications is the lack of information on location, particularly
distinguishing whether the participant was indoors or outdoors. In the
1960s and 1970s, a series of time-activity studies was conducted by
geographers interested in the influence of the economic and physical
structure of cities on travel patterns, e.g., journey to work (Hanson
& Hanson, 1981), access to facilities (Fox, 1983) or shopping
behaviour (Douglas, 1973). As such, the emphasis was on collecting
information on the geographic location of trip origins and
destinations as well as timing and mode use. Finally, the US
Department of Transportation, in conjunction with the Census Bureau,
has been collecting information on the travel activities (durations
and mode use) of a representative national sample approximately every
7 years since 1969 (US Federal Highway Administration, 1986, 1992).
A variety of methods are available for collecting data about
time-activity patterns, including interviewer-administered recall
questionnaires, self-administered real-time diaries, direct
observation and video recording. The diary techniques used in the
social sciences for eliciting time-activity data have been applied to
studies of total human exposure to air pollutants (see methodological
reviews by Robinson (1988), Ott (1989), Quackenboss & Lebowitz
(1989)). Specifically, participants are asked to complete a diary or
questionnaire regarding their activities during the designated period
(usually 12-48 h). The survey instruments used in these exposure
studies, however, depart from any single type used previously. Rather
than focusing on activity purposes or transportation exclusively, the
instruments used in exposure studies probe for changes in location or
activity that might lead to changes in the level of pollution to which
the person came into contact.
Time allocation measures for assessing exposure to air pollutants
frequently have been collected using self-completed real-time diaries.
Because this approach requests that participants record all activities
over one or more 12-h or 24-h periods, it has the potential to provide
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