Cite

APA
Li, I., Dey, A. K., & Forlizzi, J. (2011). Using context to reveal factors that affect physical activity.

Chicago/Turabian
Li, Ian, Anind K. Dey, and Jodi Forlizzi. “Using Context to Reveal Factors That Affect Physical Activity” (November 31, 2011).

MLA
Li, Ian, et al. Using Context to Reveal Factors That Affect Physical Activity. Nov. 2011.