Psychological pricing (also price ending, charm pricing) is a pricing and marketing strategy based on the theory that certain prices have a psychological impact. In this pricing method, retail prices are often expressed as just-below numbers: numbers that are just a little less than a round number, e.g. $19.99 or £2.98. There is evidence that consumers tend to perceive just-below prices (also referred to as "odd prices") as being lower than they actually are, tending to round to the next lowest monetary unit. Thus, prices such as $1.99 may to some degree be associated with spending $1 rather than $2. The theory that drives this is that pricing practices such as this cause greater demand than if consumers were perfectly rational. Psychological pricing is one cause of price points.