Frequent napping is associated with excessive daytime sleepiness, depression, pain, and nocturia in older adults: findings from the National Sleep Foundation ‘2003 Sleep in America’ Poll - Foley,D.J.; Vitiello,M.V.; Bliwise,D.L.; Ancoli-Israel,S.; Monjan,A.A.; Walsh,J.K. (Am J Geriatr Psychiatry, 2007)