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 clear ly established to date. Epidemiological assessment of these effects mi ght 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 out door time-activity patterns were tested in 168 lifelong residents (age s 17-21) of California. A test-retest design (within 5-7 days) was emp loyed. (1) Based on a set of questions (AQUES) on outdoor 'heavy' and 'moderate' activity, h/day engaged in activity were derived. Definitio n of activity levels was based on published data regarding energy expe nditure of physical activities. (2) A table format (ATAB) asked quanti tative questions for each activity engaged in. (3) A 24-hour-log (A24H ) had to be completed to indicate time spent outdoors in four levels o f activity (heavy, moderate, light, at rest) on a 'typical day' (n = 4 4). Test-retest reliability was assessed. Comparison across approaches was restricted to the subgroup of 44 students that completed all thre e approaches. Results. All approaches yielded reasonably reliable resu lts (between-test variance 13-39% of total variance, Spearman rank cor relations: 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 valu es were close to expectations when compared to published data. Conclus ions. 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 lime-activity assessment, we propose to use ATAB. F or shorter recall periods, the easier AQUES may be a reasonable altern ative, yielding similar results as ATAB. The A24H was of limited value .