Lecture Notes: Stem and Leaf Plots and Dot Plots

Introduction

• Data visualization techniques covered:
  • Stem and Leaf Plots
  • Dot Plots
• Importance: Effective in showing data distribution and shape.

Stem and Leaf Plots

Basic Concept

• Numbers are split into stems and leaves.
• Example: Data points 142 and 147
  • Stem: 14
  • Leaves: 2 and 7 (rightmost digits)
  • Presented as: 14 | 2 7
• Leaves sorted in increasing order.

Working with Decimals

• Example: Data points 16.4 and 16.9
  • Stem: 16
  • Leaves: 4 and 9
  • Context specific: Represents 16.4 and 16.9 (not 164 and 169)

Constructing a Stem and Leaf Plot

• Example: Ideal outdoor temperature data ranging from 50s to 90s
• Steps:
  1. Identify stems: 5, 6, 7, 8, 9
  2. Sort data in ascending order
  3. Enter sorted data into a calculator (stat edit)
  4. Create stem and leaf plot ensuring leaves are in increasing order

Variations

Split Stem and Leaf Plot

• Stems are repeated to split data
  • Each stem appears twice
  • Leaves 0-4 with first stem, 5-9 with second stem

Back-to-Back Stem and Leaf Plot

• Used for comparing two datasets
• Two datasets are shown on either side of a common stem
• Important: Sort both datasets in ascending order before plotting

Dot Plots

Introduction

• Simpler than stem and leaf plots
• Example: Number of cavities in a class

Construction

• List all possible values on a horizontal axis
• Place a dot above each value for each occurrence in the data
• Example data: 0, 1, 2, 3, etc.
  • Place dots corresponding to frequency of each value

Analysis

• Dot plots provide a clear picture of data distribution
• Can reveal skewness or clustering of data points

Conclusion

• Both stem and leaf plots and dot plots are valuable tools for data visualization.
• No "bad" way to display data; even simple methods can effectively convey important information about data distributions.