October 21, 2013
Lecture 6 Notes
Five number summary consists of:
1. Minimal Data set value XMIN
2. The first quartile Q1 of the data set
3. The median of Q2 of the data set MED
4. The third quartile Q3 of the data set
5. The maximal data set value XMAX
Constructing a Box-Whisker Plot
WITH NO OUTLIERS
1. Draw an evenly spaced scale that covers all of the data values
2. Using the scale, draw the box in the 1 and 3 quartiles as the sides of the box. Join the two
vertical sides with horizontal sides to form a box.
3. Using the scale as reference, draw a vertical line across the box to represent the median Q2.
Whichever box contains the average (or mean), draw a plus sign inside that corresponding box.
4. Using the scale as reference, draw a horizontal line linking Q1 to the minimal value XMIN. This
line is called the left whisker.
5. Using the scale as reference, draw a horizontal line linking Q3 to the maximal value XMAX. This
line is called the right whisker.
Suspect Outliers—How to Determine
Suspect Outliers are defined as data values that lie between the inner and outer fences. They
are plotted individually using a special symbol
Outliers are defined as data values that lie outside the outer fences. They are plotted
individually using the special symbol *
If there are outliers, the plot does not extend from min to max!
Inner and Outer Fences
Right Inner Fence is defined by RIF = Q3 + (1.5 * IQR)
Right Outer Fence is defined by ROF = RIF + (1.5 * IQR)
Left Inner Fence is defined by LIF = Q1 – (1.5 * IQR)
Left Outer Fence is defined by LOF = LIF – (1.5 * IQR)
IQR stands for interquartile range
Both RIF and ROF are the values that lie on the right-hand side of the box. They are calculated
but NOT plotted Alyssa Soubliere
October 21, 2013