1. Dukes C. Sleep in relation to education. J Roy Sanit Inst. 1905;26:41–4.
2. Claparède E. Théorie biologique du sommeil. Arch de Psychologie. 1905;4:245–349.
3. Camp C. Disturbance of sleep. J Michigan Med Soc. 1923;22:133–8.
4. Laird D. The sleep habits of 509 men of distinction. Am Med. 1931;37:271–5.
5. McGhie A, Russell S. The subjective assessment of normal sleep patterns. J Ment Sci. 1962;108:642–54.