International Journal of Epidemiology, Vol 26, 1258-1271, Copyright © 1997 by International Epidemiological Association
N Kunzli, T Kelly, J Balmes and IB Tager
BACKGROUND: Long-term effects of ambient ozone pollution are not clearly
established to date. Epidemiological assessment of these effects might
benefit from improved exposure measures. Tools to retrospectively assess
long-term time-activity patterns as a potentially important co-predictor of
true exposure have not yet been developed. METHODS: Three self-completed
questionnaires for the retrospective assessment of outdoor time-activity
patterns were tested in 168 lifelong residents (ages 17-21) of California.
A test-retest design (within 5-7 days) was employed. (1) Based on a set of
questions (AQUES) on outdoor 'heavy' and 'moderate' activity, h/day engaged
in activity were derived. Definition of activity levels was based on
published data regarding energy expenditure of physical activities. (2) A
table format (ATAB) asked quantitative questions for each activity engaged
in. (3) A 24-hour-log (A24H) had to be completed to indicate time spent
outdoors in four levels of activity (heavy, moderate, light, at rest) on a
'typical day' (n = 44). Test-retest reliability was assessed. Comparison
across approaches was restricted to the subgroup of 44 students that
completed all three approaches. RESULTS: All approaches yielded reasonably
reliable results (between-test variance 13-39% of total variance, Spearman
rank correlations: 0.68-0.86 for time spent in outdoor activities).
Population mean values differed across approaches, ranging from 1.0 (ATAB)
to an unrealistically high estimate of 3.5 (A24H) h/day. The ATAB mean
values were close to expectations when compared to published data.
CONCLUSIONS: The structure of ATAB has major advantages and mean results
were the most valid estimates compared to California population data. The
AQUES is a less transparent 'black box' measure of exposure. For long-term
retrospective time-activity assessment, we propose to use ATAB. For shorter
recall periods the easier AQUES may be a reasonable alternative, yielding
similar results as ATAB. The A24H was of limited value.
ARTICLES
Reproducibility of retrospective assessment of outdoor time-activity patterns as an individual determinant of long-term ambient ozone exposure
Division of Public Health Biology and Epidemiology, School of Public Health, University of California, Berkeley, USA.
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