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
 Determine interquartile range based on a given data set 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: IQR = Q3 − Q1.
 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 9.
 (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?

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.
 To see this, we compare the construction of histogram and kernel density estimators using these 6 data points: x_{1} = −2.1, x_{2} = −1.3, x_{3} = −0.4, x_{4} = 1.9, x_{5} = 5.1, x_{6} = 6.2 For the histogram, first the horizontal axis is divided into subintervals, or bins, which cover the range of the data.
 interquartile range (noun) The difference between the first and third quartiles; a robust measure of sample dispersion.

Outliers
 Another method often used is based on the interquartile range (IQR).
 interquartile range (noun) The difference between the first and third quartiles; a robust measure of sample dispersion.

Practice 1: Center of the Data
 Calculate the following values: Exercise 2.11.5: Sample mean = x = Exercise 2.11.6: Sample standard deviation = s_{x} = Exercise 2.11.7: Sample size = n = Use the table in section 2.11.3 to calculate the following values: Exercise 2.11.8: Median = Exercise 2.11.9: Mode = Exercise 2.11.10:First quartile = Exercise 2.11.11: Second quartile = median = 50th percentile = Exercise 2.11.12: Third quartile = Exercise 2.11.13: Interquartile range (IQR) = _____  _____ = _____ Exercise 2.11.14: 10th percentile = Exercise 2.11.15 : 70th percentile = Exercise 2.11.16: Find the value that is 3 standard deviations: a.

Outliers
 Rhode Island, Texas, and Alaska are outside the normal data range, and therefore are considered outliers in this case.
 Other methods flag observations based on measures such as the interquartile range (IQR).
 interquartile range (noun) The difference between the first and third quartiles; a robust measure of sample dispersion.

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).

Lab: Continuous Distribution
 IQR means interquartile range. ) For each part below, use a complete sentence to comment on how the value obtained from the data compares to the theoretical value you expected from the distribution in the section titled "Theoretical Distribution

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.
 For the two data sets in the test scores example (p. 62), find the following: The interquartile range.
 Compare the two interquartile ranges.