AbstractsPsychology

Previous research has demonstrated that changes in units can affect judgments and decisions. For example, people interpret quantitative information that is expressed as a larger number of small units as being larger than the same quantity expressed as a smaller number of large units. In related work, estimates of length or distance or the monetary value of goods are sometimes larger when participants use large units rather than small units. In all of this research, however, the focus has been on other phenomena (e.g., anchoring, attribute weighting, consumer behavior) rather than on the underlying relationship between numerical estimates and units. In two studies, we anticipated that participants’ estimates of physical quantities (e.g., the weight of a brick) would be larger when participants used larger units (e.g., pounds) than when they used smaller units (e.g., ounces), because their numerical answers would not be adjusted enough to compensate for differences in units. In Study 1, estimates of items’ length, weight, and volume were larger when made in larger units than when made in smaller units. This “unit effect” remained significant when we adjusted for participants’ incorrect knowledge of unit ratios and when we considered only those participants who knew the correct ratios. In addition, the unit effect was larger when participants were less familiar with the units used to make the estimates. In Study 2, participants estimated weight and volume using either familiar or unfamiliar (fictional) units. The unit effect was significant for unfamiliar units but not for familiar units. Possible mechanisms for these results are discussed and further research hypotheses are presented.