Use a stacked bar chart to compare shares across two totals
For comparing shares across two totals, use a stacked bar chart instead of a pie chart to improve readability and mitigate the single-total limit of pie charts for readers.
- purpose:select
- basis:heuristic
- task:compare
- scope:grouped-result
- chart:bar:use
- chart:pie-donut:avoid
- lever:chart-family
- operator:part-whole
- quality:readability
advice
Choose the stacked bar chart for two totals
Use a stacked bar chart when you need to compare the shares of two totals. For example, compare two polls with stacked bars rather than trying to make pie charts do a two-result comparison.
reason
Why two totals outgrow one pie
A single pie chart can only show one whole and its shares. A stacked bar chart can place two wholes into one comparable display.
Mechanism: The chart keeps both totals in the same visual structure, so readers can compare matching shares across results.
Evidence: The source says one pie chart can only show one total and its shares, and recommends a stacked bar chart if you want to compare two polls with each other (Muth, 2018).
context
Use when the comparison spans two totals
- User Goal: Compare how two totals break into shares.
- Task: Compare corresponding shares across results.
- Data: Two totals with categories that sum to 100% within each total.
- Chart Setting: Choosing between pie charts and a stacked bar chart.
- Success Criterion: Differences across the two totals are easy to compare.
exceptions
Do not use when only one total needs to be shown
Break it when: You only need to show one total and its shares. Why: The single-total limit is no longer a problem.
costs
Tradeoffs of choosing the stacked bar chart
Sacrifice: You give up the single circular whole. Risk: Using pie charts fragments the comparison across totals. Mitigation: Put both totals into one stacked bar chart when cross-total comparison is the goal.
mistakes
Common misuse of pies for two totals
Mistake: Using pie charts for a task that compares two polls or two other totals. Why it fails: One pie chart can only show one total and its shares.
check
Check whether the stacked bar wins this chart choice
Failure Sign: The design needs more than one pie to make the comparison. Quick Check: Draft the same two totals as stacked bars and compare whether matching shares are easier to inspect there. Stronger Test: Ask a reviewer which display makes the two results easier to compare and keep the stacked bar if it wins.
fix
Fix the chart choice for two totals
- Replace the pie chart approach with a stacked bar chart when comparing two totals.
- Keep both totals in the same chart instead of splitting them into separate pies.
- Use the pie chart only when the display needs to show one total and its shares.