Overview
This lecture focuses on common ways statistical graphs can be misleading and how to ensure graphs accurately represent data.
Importance of Graphs in Statistics
- Creating a graph is the first and crucial step in statistical analysis.
- Graphs provide a visual overview of data trends, typical values, and variation.
Common Ways Graphs Are Misleading
- Starting the vertical (y) axis at a value other than zero exaggerates differences.
- Using symbols or pictures instead of bars in bar charts and histograms makes frequencies unclear.
- Using bars of unequal width distorts the representation of data frequencies or categories.
- Employing 3D graphs or pie charts can make some values appear larger than they are.
How to Correct Misleading Graphs
- Always start the vertical axis at zero to avoid exaggerating differences.
- Use bars of equal width for both histograms (numerical data) and bar charts (categorical data).
- Avoid 3D graphs and pie charts; use two-dimensional representations for accuracy.
Key Terms & Definitions
- Vertical Axis (y-axis) — The axis on a graph that typically represents the variable being measured.
- Histogram — A bar graph representing the frequency distribution of numerical data.
- Bar Chart — A graph that uses bars to represent categorical data frequencies.
- Pie Chart — A circular statistical graphic divided into slices to illustrate proportions.
Action Items / Next Steps
- Review your graphs to ensure the y-axis starts at zero.
- Use only bars of equal width in your charts.
- Avoid using 3D graphics for statistical representations.