title: Statistical properties of longitudinal time-activity data for use in human exposure modeling.
abstract: Understanding the longitudinal properties of the time spent in different locations and activities is important in characterizing human exposure to pollutants. The results of a four-season longitudinal time-activity diary study in eight working adults are presented, with the goal of improving the parameterization of human activity algorithms in EPA's exposure modeling efforts. Despite the longitudinal, multi-season nature of the study, participant non-compliance with the protocol over time did not play a major role in data collection. The diversity (D)--a ranked intraclass correlation coefficient (ICC)-- and lag-one autocorrelation (A) statistics of study participants are presented for time spent in outdoor, motor vehicle, residential, and other-indoor locations. Day-type (workday versus non-workday, and weekday versus weekend), season, temperature, and gender differences in the time spent in selected locations and activities are described, and D & A statistics are presented. The overall D and ICC values ranged from approximately 0.08-0.26, while the mean population rank A values ranged from approximately 0.19-0.36. These statistics indicate that intra-individual variability exceeds explained inter-individual variability, and low day-to-day correlations among locations. Most exposure models do not address these behavioral characteristics, and thus underestimate population exposure distributions and subsequent health risks associated with environmental exposures.
authors.affiliation: US Environmental Protection Agency, Research Triangle Park, NC, USA. issacs.kristin@epa@.gov
authors.forename: Kristin
authors.initials: K
authors.lastname: Isaacs
authors.forename: Thomas
authors.initials: T
authors.lastname: McCurdy
authors.forename: Graham
authors.initials: G
authors.lastname: Glen
authors.forename: Melissa
authors.initials: M
authors.lastname: Nysewander
authors.forename: April
authors.initials: A
authors.lastname: Errickson
authors.forename: Susan
authors.initials: S
authors.lastname: Forbes
authors.forename: Stephen
authors.initials: S
authors.lastname: Graham
authors.forename: Lisa
authors.initials: L
authors.lastname: McCurdy
authors.forename: Luther
authors.initials: L
authors.lastname: Smith
authors.forename: Nicolle
authors.initials: N
authors.lastname: Tulve
authors.forename: Daniel
authors.initials: D
authors.lastname: Vallero
mesh_terms: D004781:Environmental Exposure; D006801:Humans; D008137:Longitudinal Studies