Stem and Leaf Plots, Dot Plots, and Time Series Plots

Stem and Leaf Plots

A simple method for displaying small datasets.
The rightmost digit is the leaf, and the remaining digits form the stem.
- Example:
  - In the number 14.8, 14 is the stem, and 8 is the leaf.
  - In the number 2,739, 273 is the stem, and 9 is the leaf.

Consider the US Census Bureau projection for the percentage of the population aged 65 and over for each state and the District Of Columbia.
The stems range from 8 to 17.
Create a vertical list of all stems in increasing order and draw a vertical line next to the list.
For each value in the dataset, write its leaf next to its stem.
Arrange the leaves in increasing order for each stem.

Used to compare two datasets with similar values so that the same stems can be used.
Example: Comparing course averages from an English class and a history class.
In the example provided, the course averages from the history class are higher.

A graph that provides a rough impression of the shape of a dataset.
Useful for datasets that are not too large and have some repeated values.
Example: Number of children of each of the presidents of The United States and their wives.
For each value in the dataset, a vertical column of dots is drawn.
The number of dots in the column equals the number of times the value appears in the dataset.
The dot plot indicates where the values are concentrated and where the gaps are.
In the example, the most frequent number of children is two, and only four presidents had more than six.

Used when data consists of values of a variable measured at different points in time.
Example: Dow Jones Industrial Average (reflects the prices of 30 large stocks).
The table presents the closing value at the end of each year over a period of several years.
The horizontal axis represents time, and the vertical axis represents the value of the variable being measured.
Plot the values of the variable at each of the times and connect the points with straight lines.
In the example, the average generally increased until 02/2007, dropped sharply in 02/2008, and increased after 02/2008.

Demonstration of how to use Excel to construct time series plots.
Column A: Time in years.
Column B: Closing value of the Dow Jones Industrial Average at the end of each year.
To construct the plot:
1. Select the data in Column B.
2. Select Insert > Insert Line or Area Chart icon.
3. Select the line option under the 2D Line category.
4. To put the years on the horizontal axis, click on Select Data.
5. Click the Edit button under the Horizontal axis labels.
6. Select the years in Column A.