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ACCA Strategic Professional · Advanced Performance Management · Data science and analytics

Brightwell Co's sales dashboard uses a bar chart whose vertical axis starts at 95 rather than 0, so a rise in customer satisfaction from 96 to 98 appears to be a fourfold increase in bar height. What is the principal problem with this design?

The truncated axis exaggerates the difference between values and can mislead users. Because bar length encodes magnitude, starting at 95 makes a small two-point improvement look like a dramatic increase. Bar charts can show scores, and hiding data until audit is unnecessary.

  1. AThe truncated axis exaggerates the difference and may mislead usersCorrect
  2. BThe chart should show only one bar to avoid comparison
  3. CBar charts cannot display percentages or scores
  4. DThe data should be hidden until the year-end audit

Explanation

Bars encode value by length, so starting the axis at 95 makes heights 1 and 3 units, visually a threefold-plus difference for a 2% rise. This distorts perception. Bar charts can show scores, and comparison is their purpose.

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