Dongjoo Kim and  Chang-Sik Son and  Won-Seok Kang,  Development of Sleep Quality Index Using Heart Rate.   journal   = {International Journal of Biomedical and Biological Engineering}, [online]. World Academy of Science, Engineering and Technology.
    May 2016, vol. 115(7). 405 - 409
    [viewed 24 April 2024]. Available from: https://publications.waset.org/pdf/10004859.