Describing Categorical Data

​

Subject: Statistics I

​

Unit 2: Describing Categorical Data

​

Week 2 syllabus map

1. L2.1: Describing Categorical Data - Frequency Distributions
2. AQ2.1: Activity Question 1
3. L2.2: Describing Categorical Data - Charts of Categorical Data
4. AQ2.2: Activity Question 2
5. L2.3: Describing Categorical Data - Best Practices while Graphing Data 1
6. AQ2.3: Activity Question 3
7. L2.4: Describing Categorical Data - Best Practices while Graphing Data 2
8. AQ2.4: Activity Question 4
9. L2.5: Describing Categorical Data - Mode and Median

​

How to use this week

• Solve frequency tables before looking at charts.
• For every graph question, ask:
  1. what are the categories?
  2. what are the counts or percentages?
  3. which chart type is appropriate?
  4. is the graph honest and readable?
• Keep a trap list for:
  • frequency vs relative frequency
  • count vs percentage
  • bar chart vs pie chart
  • mode vs median

​

Week 2 exam traps

• Bar heights must match values exactly.
• Categories should not overlap unless the question defines them that way.
• Relative frequency is proportion or percentage, not raw count.
• Pie chart sectors must represent parts of one whole.
• Median is not meaningful for nominal categories.
• For ordinal categories, median may be meaningful, but you must preserve order.

​

Final revision checklist

• build a frequency table from raw categorical data
• convert counts to proportions and percentages
• choose a sensible chart for categorical data
• identify misleading graphs
• explain graphing best practices clearly
• distinguish when mode and median can be used