# Section_1_4 - Section 1.4 Range IQR and Finding Outliers In...

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Math 2311 Page 1 of 5 Section 1.4 Section 1.4 – Range, IQR and Finding Outliers In earlier sections we discussed measures of center (mean and median) and measures of spread (variance and standard deviation). In this section, we will introduce more measures of spread (range and interquartile range) as well as other measures of location (percentiles). Using this information we will be able to learn more about our data and will be able to identify outliers. Rangeis found by subtracting the minimum data value from the maximum data value. This is one of the simplest measures of spread (or dispersion). One major drawback of using the range, however, is its sensitivity to outliers.Standard deviation and variance are also measurements that are not resistant to outliers. Another measure of dispersion is called the interquartile range, or IQR. The IQR is not sensitive to outliers. Before we can discuss how to determine the IQR we will need to understand some more measures of location, specifically percentiles. The most common percentiles are the 25thpercentile, the 50thpercentile and the 75thpercentile. Q1(Quartile 1) is the 25thpercentile of ordered data or median of lower half of ordered data. Median (Q2) is 50thpercentile of ordered data. Q3(Quartile 3) is the 75thpercentile of ordered data or median of upper half of ordered data. Note that half of the data will fall between Q1 and Q3.