JONES KHS, ELLIS J, VON SCHANTZ M, SKENE DJ, DIJK D, ARCHER SN. Age‐related change in the association between a polymorphism in the PER3 gene and preferred timing of sleep and waking activities. Journal of Sleep Research. 2007 Feb 19;16(1):12–6. doi: 10.1111/j.1365-2869.2007.00561.x.