231114 - Section 1.4 Range IQR and Finding Outliers In earlier sections we discussed measures of center(mean and median and measures of spread(variance

# 231114 - Section 1.4 Range IQR and Finding Outliers In...

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Section 1.4 – Range, IQR and Finding Outliers 1 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. The minimum is the smallest data value. The maximum is 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 25 th percentile, the 50 th percentile and the 75 th percentile. Quartile 1 (Q1) is the 25 th percentile of ordered data or median of lower half of ordered data. Quartile 2 (Q2) , is the median or 50 th percentile of ordered data. Quartile 3 (Q3) is the 75 th percentile of ordered data or median of upper half of ordered data. Note that half of the data will fall between Q1 and Q3.