Many consumers believe 36 months is longer than 3 years

"As a consumer, would your preference for a dishwasher depend on whether its warranty level is expressed in months rather than years?" write authors Mario Pandelaere (Ghent University, Belgium), Barbara Briers (Tilburg University, the Netherlands), and Christophe Lembregts (Ghent University, Belgium).

To most consumers, the answer is "yes." The difference between an 84-month and a 108-month warranty looks bigger than the difference between a seven-year and a nine-year warranty, despite the fact that both differences are exactly the same.

"Qualitative information can usually be specified in alternative units," the authors write. "In many cases, however, the specific unit in which information is described is arbitrary. For instance, product quality ratings may be expressed on a scale from 0 to 10 or on a scale from 0 to 100," the authors write. "People typically fail to realize that the unit of quantitative information is arbitrary. They just focus on the number of scale units used to express a certain difference."

As a result, higher numbers seem to represent bigger quantities. This "unit effect" is the reason why consumers perceive a bigger difference between ratings 90 and 95 out of 100 than they do between a 9 or 9.5 out of 10.

In an additional study, the authors found that the unit effect can be used to encourage healthy food choices. In one experiment, participants exiting the lab were offered the choice between a complimentary apple or a Twix® bar. The energy content of these two choices was either expressed in Kilojoules (247 for the apple versus 1029 for the Twix®) or Kilocalories (59 for the apple versus 246 for the Twix®). "Participants more often chose the apple when the energy content was expressed in Kilojoules than in Kilocalories as the former difference (782 Kilojoules) looks much bigger in the latter one (187 Kilocalories).

However, the authors found that the effect was not replicated when people pay close attention to specific attribute information or when people are reminded of the arbitrary nature of the unit in which information is expressed.