Quartiles + Box and Whisker Plots
Quartiles Step 1: Find the Median. This is called Q2, or the second quartile. Step 2: Split the first half into 2 equal groups (same rules as finding the median). The middle value is called Q1, or the first quartile. Step 3: Find median of top half of numbers (Q3). You have split the numbers into 4 quarters.
12, 15, 18, 24, 26, 29, 30, 32 Q2 = average of 24 and 26 Q2 = 25
12, 15, 18, 24, 26, 29, 30, 32 Q2 = 25 Q1 = 16.5Q3 = 29.5
Box and Whisker Plot 1) Draw a number line from the lowest to highest value 2) Draw a line above Q1, Q2 and Q
Box and Whisker Plot 2)Draw a line above Q1, Q2 and Q3 3) Attach lines to make the “box”
Box and Whisker Plot 2) Draw a line above Q1, Q2 and Q3 3) Attach lines to make the “box”
Box and Whisker Plot 4) Draw a line over the minimum and maximum values 5) Draw “whiskers”
Example 6, 8, 12, 14, 17, 19, 21, 24, 25 Q2 Q1 = 10 Q3 = 22.5
Measures of Dispersion Variation Interval: [Xmin, Xmax] 100% of data in this interval Range: Xmax – Xmin Interquartile Interval: [Q1, Q3] 50% of data in this interval Interquartile Range: Q3 – Q1