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: - Put your data in a list from small to large
- Find the median (the value in the middle of the dataset)
- if there are 2 data values average them together to get the median
- 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.
- Find the Inter Quartile Range: Q3-Q1
- Apply the Interquartile range to the formula below to ensure there are no outliers
- If there are outliers use the IQR (inter quartile range) to get the min and max values accepted as normal values
- Put any outliers on the plot as dots.
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