interquartile range
The difference between the first and third quartiles; a robust measure of sample dispersion.
Examples of interquartile range in the following topics:

Interquartile Range
 The interquartile range (IQR) is a measure of statistical dispersion, or variability, based on dividing a data set into quartiles.
 The interquartile range is equal to the difference between the upper and lower quartiles:
 This is the Interquartile range, or IQR.
 Unlike (total) range, the interquartile range has a breakdown point of 25%.
 In other words, since this process excludes outliers, the interquartile range is a more accurate representation of the "spread" of the data than range.

Measures of Variability
 There are four frequently used measures of variability: range, interquartile range, variance, and standard deviation.
 The interquartile range (IQR) is the range of the middle 50% of the scores in a distribution.
 The interquartile range is therefore 2.
 A related measure of variability is called the semiinterquartile range.
 The semiinterquartile range is defined simply as the interquartile range divided by 2.

Exercises
 : mean, median, mode, trimean, geometric mean, range, interquartile range, variance, standard deviation
 (AM#8) What is the range of the AngerIn scores?
 What is the interquartile range?
 (SL#2) Find the mean, median, standard deviation, and interquartile range for the leniency scores of each of the four groups.
 (AT#7) What are the standard deviation and the interquartile range of the d0 condition?

Practice 1: Center of the Data
 Exercise 2.11.13: Interquartile range (IQR) = _____  _____ = _____

Box plots, quartiles, and the median
 The total length of the box, shown vertically in Figure 1.25, is called the interquartile range (IQR, for short).

The Density Scale
 In addition to the points themselves, box plots allow one to visually estimate the interquartile range.
 A range of data clustering techniques are used as approaches to density estimation, with the most basic form being a rescaled histogram.
 For the histogram, first the horizontal axis is divided into subintervals, or bins, which cover the range of the data.

Lab: Continuous Distribution
 IQR means interquartile range. )

Measures of the Location of the Data
 The interquartile range is a number that indicates the spread of the middle half or the middle 50% of the data.

Graphs of Qualitative Data
 Median, measures of shape, measures of spread such as the range and interquartile range, require an ordered data set with a logical lowend value and highend value.

Outliers
 Other methods flag observations based on measures such as the interquartile range (IQR).
 Rhode Island, Texas, and Alaska are outside the normal data range, and therefore are considered outliers in this case.