New Stats 1 Tips‎ > ‎

Creating Box Plots

posted Mar 5, 2010, 2:43 PM by Prof Kiernan   [ updated Feb 6, 2014, 5:59 AM ]

How to make a Box plot by hand:

1. Find the 5-number summary (smallest value, Q1, Median, Q3, & the largest value)

2. Construct a scale with values that include the minimum and maximum values

3. Construct a box extending from the first quartile to the third quartile and draw

a line in the box at the median value

4. Draw lines extending outward from the box to the minimum and the maximum

data values and you're done!




How to make a Box Plot using the calculator:
Put data into list #1:

Press STAT

Press ENTER (1:Edit)

Put in variable under list 1 L1 

Press ENTER

(continue the last two steps until you have added all of the variables in your list)

Get the 5 number summary:

Press STAT

Press CALC           

Press 1 (1: 1-Var Stat)             

Press 2nd            

Press L1 (or the name of the list that you have put your information in)

Press ENTER

Press Down arrow (the last 5 things in the list are the 5 number summary)


To see the Box Plot:

Press 2nd

Press Y=

Press ENTER

Press ENTER

Press DOWN ARROW

Press RIGHT ARROW (till you highlight the box plot with the dots)

Press ENTER

Press ZOOM

PRESS 9 (9: zoom stat)


Voila! You have your box plot!



To find the Q1, Median, and Q3 by hand:

  1. Put your data in a list from small to large
  2. Find the median (the value in the middle of the dataset)
    • if there are 2 data values average them together to get the median
  3. Find the first and second Quartiles (Q1 & Q3) the same way:
    • make 2 separate data sets and  find the middle value of each new datasets.
  4. Find the Inter Quartile Range: Q3-Q1
  5. Apply the Interquartile range to the formula below to ensure there are no outliers
    1. If there are outliers use the IQR (inter quartile range) to get the min and max values accepted as normal values
    2. Put any outliers on the plot as dots.



 
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