The interquartile range (IQR), also called the midspread or middle fifty, is a measure of statistical dispersion, being equal to the difference between the upper and lower quartiles. The interquartile range is the upper quartile (75th percentile) minus (-) the lower percentile (75th percentile).The interquartile range uses 50% of the data.
The interquartile range is a value that is the difference between the upper quartile value and the lower quartile value. Coach Taylor can use the interquartile range to summarize the overall accuracy of his players. To find the quartiles of this data set use the following steps: 1  Order the data from least to greatest. The interquartile range is a value that is the difference between the upper quartile value and the lower quartile value. To find the interquartile range, simply take the upper quartile and subtract the lower quartile. To unlock this lesson you must be a Study.com Member. An Alternative Definition for IQR. In some texts, the interquartile range is defined differently. It is defined as the difference between the largest and smallest values in the middle 50% of a set of data. To compute an interquartile range using this definition, first remove observations from the lower quartile. Then, remove observations from the upper quartile. Then, from the remaining observations, compute the difference between the largest and smallest values. Q3 is the middle value in the second half of the data set. Again, since the second half of the data set has an even number of observations, the middle value is the average of the two middle values; that is, Q3 = (6 + 7)/2 or Q3 = 6.5. The interquartile range is Q3 minus Q1, so IQR = 6.5 - 3.5 = 3. In descriptive statistics, the interquartile range (IQR), also called the midspread or middle fifty, is a measure of statistical dispersion, being equal to the difference between the upper and lower quartiles, IQR = Q 3 − Q 1. The interquartile range is often used to find outliers in data. Outliers are observations that fall below Q1 - 1.5(IQR) or above Q3 + 1.5(IQR). To find the interquartile range, simply take the upper quartile and subtract the lower quartile: 7.5 - 2.5 = 5. The interquartile range for this data set is 5. That means that the majority of the group can make about five out of ten free throw shots. Since the quartiles divide the data set into four equal groups, there are a few things to note about the data set. The interquartile range is a value that is the difference between the upper quartile value and the lower quartile value. To find the interquartile range, simply take the upper quartile and subtract the lower quartile. To unlock this lesson you must be a Study.com Member. Interquartile range. In descriptive statistics, the interquartile range, also called the midspread or middle fifty, is a measure of statistical dispersion, being equal to the difference between the upper and lower quartiles, IQR = Q3 − Q1.  Difference between the first quartile (25th percentile) and the third quartile (75th percentile) of an ordered range of data. It contains middle 50 percent of the distribution and is unaffected by extreme values. Half of this range (25 percent or the distribution) is called semi-interquartile range. 
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