STAT 201 Chapter Notes - Chapter 2.5: Interquartile Range, Quartile, Box Plot
19 Sep 2016
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Median is a special case of a more general set of measures of a position called percentiles. Pth percentile= a value such that p percent of the observations fall below or at the value. 50th percentile is referred to as the mean. First quartile has p=25, so it"s the 25th percentile: lowest 25% of data fall below it. Second quartile has p=50, so it"s the 50th percentile (median) Third quartile has p=75, so it"s the 75th percentile: highest 25% of data fall above it. Quartiles are used to define a measure of variability that"s more resistant than the range and standard deviation. Summarizes range for middle half of data: middle 50% of observations fall between q1 and q3. Interquartile range (iqr)= distance from quartile 1 to quartile 3: iqr=q3-q1. The more varied the data, the larger the iqr tends to be.
