Tokens should be durable, convenient to store and handle, easy to carry around and deliver, and difficult to steal or counterfeit. Examples in research have included poker chips (which can be color-coded based on their value), tickets, stars, points on a tally sheet or counter, check marks, punched holes on cards, currency or coins individually devised for the program, foreign coins, and plastic credit cards (Kazdin, 1977). The items that are used will vary depending on the setting, the population, and special problems that may arise in that context. For example, persons awarding or fining Joe points might be required to initial his index card each time they do so in order to prevent him from cheating.