Till Roenneberg et al., “A Marker for the End of Adolescence,” Current Biology 14, no. 24 (2004): R1038–1039.
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Till Roenneberg et al., “Epidemiology of the Human Circadian Clock,” Sleep Medicine Reviews 11, no. 6 (2007): 429–438; See also Ana Adan et al., “Circadian Typology: A Comprehensive Review,” Chronobiology International 29, no. 9 (2012): 1153–1175.