title: Circadian analysis of large human populations: inferences from the power grid.
abstract: Few, if any studies have focused on the daily rhythmic nature of modern industrialized populations. The present study utilized real-time load data from the U.S. Pacific Northwest electrical power grid as a reflection of human operative household activity. This approach involved actigraphic analyses of continuously streaming internet data (provided in 5 min bins) from a human subject pool of approximately 43 million primarily residential users. Rhythm analyses reveal striking seasonal and intra-week differences in human activity patterns, largely devoid of manufacturing and automated load interference. Length of the diurnal activity period (alpha) is longer during the spring than the summer (16.64 h versus 15.98 h, respectively; p < 0.01). As expected, significantly more activity occurs in the solar dark phase during the winter than during the summer (6.29 h versus 2.03 h, respectively; p < 0.01). Interestingly, throughout the year a "weekend effect" is evident, where morning activity onset occurs approximately 1 h later than during the work week (5:54 am versus 6:52 am, respectively; p < 0.01). This indicates a general phase-delaying response to the absence of job-related or other weekday morning arousal cues, substantiating a preference or need to sleep longer on weekends. Finally, a shift in onset time can be seen during the transition to Day Light Saving Time, but not the transition back to Standard Time. The use of grid power load as a means for human actimetry assessment thus offers new insights into the collective diurnal activity patterns of large human populations.
authors.affiliation: Department of Biological Sciences, Kent State University , Kent, OH , USA.
authors.forename: Adam C
authors.initials: AC
authors.lastname: Stowie
authors.forename: Mario J
authors.initials: MJ
authors.lastname: Amicarelli
authors.forename: Caitlin J
authors.initials: CJ
authors.lastname: Crosier
authors.forename: Ryan
authors.initials: R
authors.lastname: Mymko
authors.forename: J David
authors.initials: JD
authors.lastname: Glass
mesh_terms: D056044:Actigraphy; D001331:Automation; D001683:Biological Clocks; D001831:Body Temperature; D002940:Circadian Rhythm; D004560:Electricity; D004569:Electroencephalography; D004651:Employment; D006801:Humans; D020407:Internet; D008027:Light; D015205:Northwestern United States; D011210:Power Plants / Q000706:statistics & numerical data*; D012621:Seasons; D012890:Sleep / Q000502:physiology*; D013472:Sunlight; D013997:Time Factors; D014481:United States
keywords: Circadian; human; population activity analysis; power grid