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

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.