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Section 1.4 – Range, IQR and Finding Outliers 1Section 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. The minimumis the smallest data value. The maximumis the largest data value. The range of a set of data is: Maximum – Minimum (Sensitive to outliers.) Another measure of dispersion is called the interquartile range, or IQR. 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. Quartile 1 (Q1) is the 25thpercentile of ordered data or median of lower half of ordered data. Quartile 2 (Q2), is the median or 50thpercentile of ordered data. Quartile 3 (Q3)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.