Timo Christophersen Udo Konradt Reliability, validity, and sensitivity of a single-item measure of online store usability. 269-280 2011 69 Int. J. Hum.-Comput. Stud. 4 http://dx.doi.org/10.1016/j.ijhcs.2010.10.005 db/journals/ijmms/ijmms69.html#ChristophersenK11