definition of iqr in math
The IQR is the length of the box in your box-and-whisker plot. An outlier is any value that lies more than one and a half times the length of the box from either end of the box.
Definition: Interquartile range is the measure of dispersion which is the difference in the values of two quartiles. The Lower Quartile is denoted as Q 1 and the Upper Quartile is denoted as Q 3. The interquartile range is Q 3 - Q 1. Semi Interquartile range is the midpoint of the interquartile range. In other words, it is one-half of the difference between the third quartile and the first quartile. Therefore, Semi-Interquartile range = $\frac{Q_{3}-Q_{1}}{2}$. Where Q 1 and Q 3 are the upper and lower quartiles respectively.