Tamura A, Tomita T, Oshima T, Toyoshima F, Yamasaki T, Okugawa T, Kondo T, Kono T, Tozawa K, Ikehara H, Ohda Y, Fukui H, Watari J, Miwa H.  Prevalence and Self-recognition of Chronic Constipation: Results of an Internet Survey.  J Neurogastroenterol Motil 2016;22:677-685.  https://doi.org/10.5056/jnm15187