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9.5: Misleading Visualizations

  • Page ID
    142425

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    9.5 Misleading Visualizations — A Case Study

    🏛 Real-World Example — The Challenger O-Ring Data

    On January 27, 1986, the night before the Space Shuttle Challenger launch, engineers at Morton Thiokol presented data to NASA managers about O-ring erosion and launch temperature. Their concern: the forecast launch temperature of 26°F was far colder than any previous launch, and they believed cold increased O-ring failure risk.

    The data supported their concern — but the graphs they used nearly concealed it. Engineers had plotted only the flights that showed O-ring damage, omitting flights with no damage. When you exclude the undamaged cases, there is no visible temperature trend — you have removed the comparison. A plot of all flights shows the relationship clearly: damage was concentrated in cold launches.

    NASA managers, seeing graphs that showed no clear trend, asked engineers to prove cold caused failure. Engineers could not make their case from the data as presented. The launch proceeded. Challenger was destroyed 73 seconds after liftoff due to O-ring failure in the cold.

    The lesson: Incomplete data, cherry-picked cases, or poorly constructed graphs can lead experienced engineers to wrong conclusions — with fatal consequences. Plotting all relevant data honestly is not just good practice. It is an ethical obligation.

    Four Ways Graphs Mislead

    1. Truncated y-axis. Starting at a non-zero value compresses or exaggerates variation. A 5% data change can appear to be a 500% change. Start at zero unless there is a stated, defensible reason.
    2. Cherry-picked data range. Plotting only the "good" part of the operating range hides constraint violations that appear elsewhere. Plot the full relevant range.
    3. Wrong chart type. A bar chart of a continuous power sweep misrepresents the continuous nature of the relationship. Match chart type to data structure.
    4. Missing units on axes. A graph of "Force" vs. "Angle" with no units cannot be verified, reproduced, or trusted. Axis labels without units are incomplete.

    This page titled 9.5: Misleading Visualizations was last modified on Thu, 24 Sep 2026 17:36:31 GMT and is shared under a CC BY-NC license and was authored, remixed, and/or curated by .

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