Ophthalmic statistics note 1: unit of analysis
Catey Bunce, Krishna V Patel, Wen Xing, Nick Freemantle, Caroline J Doré, On behalf of the Ophthalmic Statistics Group
British Journal of Ophthalmology Mar 2014, 98 (3) 408-412; DOI: 10.1136/bjophthalmol-2013-304587