Angela Lee Duckworth, Teri A. Kirby, Eli Tsukayama, Heather Berstein and K. Anders Ericsson. Deliberate Practics Spells Success. Social Psychological and Personality Science 2011 2: 174 originally published online 4 October 2010 DOI: 10.1177/1948550610385872
Galla, Brian M, Benjamin D Plummer, Rachel E White, David Meketon, Sidney K D’Mello, and Angela L Duckworth. “The Academic Diligence Task (ADT): Assessing Individual Differences in Effort on Tedious but Important Schoolwork.” Contemporary Educational Psychology 39, no. 4 (October 1, 2014): 314–25. doi:10.1016/j.cedpsych.2014.08.001.
Herzfeld, David, Shadmehr, Reza. “Motor Variability Is Not Noise but Grist for the Learning Mill.” Nature Neuroscience 17, no. 2. Accessed February 24, 2015.http://www.seas.harvard.edu/motorlab/Reprints/Wu et al. - 2014 - Temporal structure of motor variability is dynamic_NV.pdf.