ABSTRACT
This chapter shows that the statistics that measure the amount of variability in a set of scores called measures of variability. It explores the range of scores and its limitations when describing a data with outliers. The chapter focuses on the concepts and computation of interquartile range which measures the range of the middle 50% of the scores. In addition to the measures of central tendency, range and interquartile range are used to measure how much scores vary around the mean or median of numerical data. For instance, if all the participants who take a test earn the same score, there is no variability. A group of statistics called measures of variability are designed to concisely describe the amount of variability in a set of scores. A better measure of variability is the interquartile range. The interquartile range may be thought of as a first cousin of the median.
