January 14, 2008
[
LECTURE 3
]
1
I.
Stemplots:
How to make a stemplot:
1)
Separate each observation into a
stem,
consisting of all but
the final (rightmost) digit, and
a
leaf,
which is that remaining final digit. Stems may have as many digits as needed, but
each leaf contains only a single digit.
2)
Write the stems in a vertical column with the smallest value at the top, and draw a
vertical line at the right of this column.
3)
Write each leaf in the row to the right of its stem, in increasing order out from the stem.
Example:
Original data:
9, 9, 22, 32, 33, 39, 39, 42, 49, 52, 58, 70
II.
Time plots
(Line graphs):
Use when there is a meaningful sequence, like time. The line connecting the points helps
emphasize any change over time.
Example:
Time always goes on the horizontal, or x, axis. The variable of interest— here “retail
price of fresh oranges”—goes on the vertical, or y, axis.