Data Visualization Methods

Overview

• Bar Charts, Pie Charts, Histograms, Stem Plots, and Time Plots are tools for displaying data.
• Bar Charts & Pie Charts: Used for categorical data.
• Histograms, Stem Plots & Time Plots: Used for quantitative data.

Bar Charts & Pie Charts

Pie Charts

• Show relative size of each value in relation to the whole.

Bar Charts

• Display frequency on one axis, values of categorical variable on the other.
• Tallying information.

Quantitative Data Visualizations

Histograms

• Display distribution of data collected.
• Frequency (count) on one axis, variable measured on the other.
• Example: Interval 100-110 with height 8 means 8 people weigh between 100 and 110 pounds.
• Frequency distributions can be written in table format.
• Interval Inclusion: Each interval does not include the right endpoint.
• Relative Frequency Distribution: Shows proportion of values in each interval relative to the whole.
  • Total data values sum to 50, each value divided by this sum to get relative frequency.
  • Sum of relative frequencies should equal 1.
  • Can be converted to percentages.
  • Histograms can be converted to proportion histograms.

Stem Plots

• Similar to histograms, but show each data point.
• Consist of stems and leaves.
  • Leaf: Last number.
  • Stem: All other numbers except the last one.
  • Example: 117 -> Stem: 11, Leaf: 7
  • Example: 69 -> Stem: 6, Leaf: 9
• Stems go from low to high, leaves extend from low to high.
• Split Stem Plot: To handle too many leaves, duplicate each stem; run first from 0-4, second from 5-9.
• Trimming Leaves: To handle too many stems; remove the last digit.
  • Example: 201 -> Trimmed: 20 -> New leaf: 0, New stem: 2.
  • Read trimmed data appropriately.
• Back-to-Back Stem Plot: Compare two distributions using same stems (e.g., males vs. females).

Time Plots

• Show how a variable changes over time.
• Time on x-axis, variable values on y-axis.