Selected Publications

  1. Di, J., Spira, A., Bai, J., Urbanek, J., Leroux, A., Wu, M., Resnik, S., Simonsick, E., Ferrucci, L., Schrack, J., and Zipunnikov, V.. Joint and individual representation of domains of physical activity, sleep, and circadian rhythmicity. Statistics in Biosciences. 2019.
  2. Johns, J., Di, J., Merikangas, K., Cui, L., Swendsen, J., and Zipunnikov, V.. Fragmentation as a novel measure of stability in normalized trajectories of mood and attention measured by ecological momentary assessment. Psychological Assessment. 2019.
  3. Leroux, A., Di, J., Smirnova, E., Mcguffey, E., Cao, Q., Bayatmokhtari, E., Tabacu, L., Zipunnikov, V., Urbanek, J., Crainiceanu, C.. Organizing and analyzing the activity data in NHANES. Statistics in Biosciences. 2019.
  4. Schrack, J., Kuo, P., Wanigatunag, A., Di, J., Simonsick, EM., Spira, A., Ferrucci, L., and Zipunnikov, V.. Active-to-sedentary behavior transition, fatigability, and physical functioning in older adults. The Journal of Gerontology: Series A. 2019.
  5. Grigsby, M., Di, J., Leroux, A., Zipunnikov, V., Xiao, L., Crainiceanu, C., and Checkley, W.. Novel metrics for growth model selection. Emerging Themes in Epidemiology. 2018.
  6. Urbanek, J., Spira, A., Di, J., Leroux, A., Crainiceanu, C., and Zipunnikov, V.. Epidemiology of objectively measured bedtime and chronotype in US adolescents and adults: NHANES 2003 - 2006. Chronobiology International. 2018.
  7. Varma, V., Dey D., Leroux A., Di, J., Urbanek, J., Xiao, L., and Zipunnikov, V.. Total volume of physical activity: TAC, TLAC, or TAC(\(\lambda\)). Preventive Medicine. 2018.
  8. Di, J., Leroux, A., Urbanek, R., Varadhan, J., Spira, A., Schrack, J., and Zipunnikov, V.. Patterns of sedentary and active time accumulation are associated with mortality in US adults: The NHANES study. bioRxiv: 182337.
  9. Varma, V., Dey D., Leroux A., Di, J., Urbanek, J., Xiao, L., and Zipunnikov, V.. Re-evaluating the effect of age on physical activity over the lifespan. Preventive Medicine. 2017..

A full list of my publications can be found on my Google Scholar page.


  1. actigraphy. (R package). Feature extraction from minute level actigraphy data. [Github].
  2. cdHOTS. (R package). Construct and decompose higher order tensorian statistics.[Github]
  3. actigraphy-profiles. (R Shiny App). A visualization tool for displaying minute-level actigraphy profiles (More features to be online). [Github]
  4. ActFrag. (R package). Activity fragmentation metrics extraced from minute level actigraphy data. [Github] [CRAN]