Few, if any studies have focused on the daily rhythmic nature of modern industrialized populations. The present study involved actigraphic analyses of continuously streaming electrical load data from a human subject pool of approximately 43 million primarily residential users in the U.S. Pacific Northwest as a reflection of daily household activity. 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 during the weekend 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 Daylight 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.
Dr. J. David Glass
Mr. Adam Stowie