interquartile range A quantitative confidence value that refers to the upper and lower values defining the central 50 percent of observations. The boundaries are equal to the 25th and 75th percentiles. The interquartile range can be depicted in a box and whiskers plot. WEB: http://www.uptodate.com/contents/glossary-of-common-biostatistical-and-epidemiological-terms Yongqun He quantitative confidence value