The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants.
Level 4 - case-series / case-control
Cross-sectional population survey (graded by design analogy for exposure epidemiology)
PubMed 11477521 · doi:10.1038/sj.jea.7500165
What was done
The National Human Activity Pattern Survey (NHAPS) collected 24-hour retrospective time-activity diaries and questionnaire data via computer-assisted telephone interviewing (CATI) between September 1992 and September 1994. The probability-based survey sampled participants across all ages in the 48 contiguous United States across all 10 EPA regions (340 to 1,713 respondents per region), recording start and end times for microenvironmental locations and activities. The household completion rate was 63% (n=9,386).
What was found
Respondents spent an average of 87% of their time inside enclosed buildings and approximately 6% of their time in enclosed vehicles. These time-use proportions remained consistent across US regions, Canada, and compared to historical California data from the late 1980s. California residents showed a decrease in reported exposure to environmental tobacco smoke (ETS) between the late 1980s and mid-1990s. In both California and nationwide, the majority of reported ETS exposure time occurred in residential settings.
Why it matters
This study provides foundational baseline data demonstrating that Americans spend roughly 93% of their time in enclosed microenvironments (buildings and vehicles), establishing indoor environments as the primary determinant of human pollutant exposures for environmental risk modeling.
Limits
The survey relied on single-day 24-hour retrospective recall, which is vulnerable to recall error. Only telephone-accessible households in the contiguous US were sampled, with a 37% non-response rate that may introduce selection bias. Direct pollutant concentrations were not measured; exposure was inferred from reported time spent in microenvironments and proximity to smokers.
Cited by
- context Men aged 20 to 30 spend less time outdoors than prison inmates do.