Deltiology (from Greek δελτίον, deltion, diminutive of δέλτος, deltos, "writing tablet, letter"; and -λογία, -logia) is the study and collection of postcards. Professor Randall Rhoades of Ashland, Ohio, coined a word in 1945 that became the accepted description of the study of picture postcards. It initially took about 20 years for the name to appear in a dictionary. Compared to philately, the identification of a postcard's place and time of production can often be an impossible task because postcards, unlike stamps, are produced in a decentralised, unregulated manner. For this reason, some collectors choose to limit their acquisitions to cards by specific artists and publishers, or by time and location.