1. Duffy, J., Dijk, D., Hall, E. & Czeisler, C. Relationship of endogenous circadian melatonin and temperature rhythms to self-reported preference for morning or evening activity in young and older people. J. Investig. Med. Off. Publ. Am. Fed. Clin. Res. 47, 141–150 (1999).
2. Duffy, J. F., Rimmer, D. W. & Czeisler, C. A. Association of intrinsic circadian period with morningness–eveningness, usual wake time, and circadian phase. Behav. Neurosci. 115, 895 (2001).
3. Horne, J. A. & Ostberg, O. A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms. Int. J. Chronobiol. 4, 97–110 (1975).
4. Broms, U. et al. Long-term consistency of diurnal-type preferences among men. Chronobiol. Int. 31, 182–188 (2014).
5. Koskenvuo, M., Hublin, C., Partinen, M., HEIKKILÄ, K. & Kaprio, J. Heritability of diurnal type: a nationwide study of 8753 adult twin pairs. J. Sleep Res. 16, 156–162 (2007).