1. Jackson ML, Bruck D. Sleep Abnormalities in Chronic Fatigue Syndrome/Myalgic Encephalomyelitis: A Review. Journal of Clinical Sleep Medicine?: JCSM?: Official Publication of the American Academy of Sleep Medicine. 2012;8(6):719-728. doi:10.5664/jcsm.2276.<br /><br />2. Meeus M, Goubert D, De Backer F, Struyf F, Hermans L, Coppieters I, De Wandele I, Da Silva H, Calders P. Heart rate variability in patients with fibromyalgia and patients with chronic fatigue syndrome: a systematic review. Semin Arthritis Rheum. 2013 Oct;43(2):279-87. doi: 10.1016/j.semarthrit.2013.03.004. Epub 2013 Jul 6.<br /><br />3. Tak LM, Riese H, de Bock GH, Manoharan A, Kok IC, Rosmalen JG. As good as it gets? A meta-analysis and systematic review of methodological quality of heart rate variability studies in functional somatic disorders. Biol Psychol. 2009 Oct;82(2):101-10. doi: 10.1016/j.biopsycho.2009.05.002. Epub 2009 May 20. <br />a. This is an older article. It is being referenced because it contains a table designating elements that should be reported in studies of heart rate variability.