Multipoint scales: Mean and median differences and observed significance levels

Researchers in human‐computer interaction (HCI) often use discrete multipoint scales (such as 5‐ or 7‐point scales) to measure user satisfaction and preference. Many knowledgeable authors state that the median is the appropriate measure of central tendency for such ordinal scales, although others challenge this assertion. This article introduces a new point of view, based on a human factors consideration. When decision makers read a usability report or attend a briefing, they may make decisions based on the magnitude of the difference between the measures of central tendency for key dependent variables. A major criterion that should affect the choice of presenting means or medians is the strength of the relationship between this difference and the observed significance levels of appropriate statistical tests. The results from two series of “real‐world” usability studies showed that the mean difference correlated more than the median difference with the observed significance levels (both parametric and nonparametric) for discrete multipoint scale data. Therefore, for these scales in this measurement context, the mean can be a better measure of central tendency than the median. The results also provided evidence that mean differences for 7‐point scales correlate more strongly with observed significance levels than those for 5‐point scales.