Reproducibility of retrospective assessment of outdoor time-activity patterns as an individual determinant of long-term ambient ozone exposure

Abstract

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.