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Claude
761e048811
The source-request loop paid for itself immediately — two of the five corrected something rather than confirming it. The Economist piece settles V1, the riskiest live claim, but our note had over-claimed: truncating the scale is its *first* example, not one of "several." Note rewritten to quote her. The same article turned out to contain a dual-axis chart she caught herself on, now cited. Datawrapper's color-scale part 1 refuted the assumption behind a queued sin outright: it makes no argument against rainbow scales and endorses multi-hue sequential gradients. The rainbow entry is now marked as having no verified source at all, rather than ample backing. The dual-axis post independently draws the same line we drew last turn — of four uses only the alternative-scale case survives, their example being F against C — and led to two references worth more than the blog post: the Isenberg et al. study that tested dual-scale charts, and Few's article working through the cases. Both ship without full metadata rather than guessed metadata; queued. Pie and stacked posts gave verbatim support, plus one correction: a 100%-stacked chart has two readable baselines, not one. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01ULE5RRxdQE1ebwefEd2eCM
71 lines
3.3 KiB
Markdown
71 lines
3.3 KiB
Markdown
# Datawrapper — "Why not to use two axes, and what to use instead"
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Lisa Charlotte Muth, `blog.datawrapper.de/dualaxis/`, published **8 May 2018**,
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intro updated **July 2026**. Supplied as PDF, read 2026-08-05.
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Answers queue rows 2 and (partly) 1.
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## The July 2026 revision, verbatim
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> We originally published this article in May 2018 to explain why you couldn't
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> create dual-axis charts in Datawrapper. Since then, we've changed our minds.
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> We've learned that in some cases, dual-axis charts really are the best way to
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> show the data — and that people who've learned to read them correctly (in
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> financial services, for example) aren't misled by them. […] But all the issues
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> this original article pointed out are still valid. A general audience is
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> indeed likely to misread dual-axis charts.
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So: audience-dependent, not a reversal. They now ship the feature on a Business
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plan and kept the article standing. They also link a newer piece, "What to
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consider when creating dual-axis charts" (23 July 2026), not supplied here.
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## They draw the same line we drew
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The article lists four reasons people reach for dual axes, then says:
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> of these four use cases, we think that only the last dual axis chart can be
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> used without being potentially misleading, since it only uses the second
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> Y-axis to show an alternative scale and not a second data series.
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The fourth case is **Fahrenheit and Celsius on one series** — the same example
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our sin page arrived at independently. Their test and ours match: the sin is a
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second *data series*, not a second *scale*.
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## The three problems
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1. **"Zero baselines at different heights can mislead."** The proportions are
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arbitrary. Their worked example: German vs global GDP looks like it rises at
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the same rate; extended to zero, global rose 80% and Germany 40%.
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2. **"Even zero baselines at the same height can mislead"** — "humans have a
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tendency to set things in relation if they're close-by." Readers conclude
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German GDP exceeded global GDP, then crossed in 2011.
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3. **"They're just hard to read."**
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Nutshell line: *"The scales of dual axis charts are arbitrary and can therefore
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(deliberately) mislead readers about the relationship between the two data
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series."*
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## The empirical source behind it — worth citing directly
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Isenberg, Bezerianos, Dragicevic & Fekete (2011), *A Study on Dual-Scale Data
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Charts*. 15 participants, four chart types; the dual-axis ("superimposed")
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chart was quoted as:
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> We found across the board that the superimposed chart performed poorly both
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> in terms of accuracy and time. […] it was ranked lowest by all but one
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> participant. Participants called it very confusing and demanding too much
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> concentration or reflection to decipher the non-monotonic and discontinuous
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> nature of the two scales.
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Added to the reference list as `isenberg2011`. Venue/DOI still needed — queued.
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Also flagged: Stephen Few, *Dual-Scaled Axes in Graphs: Are They Ever the Best
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Solution?*, which per Datawrapper concludes he "cannot think of a situation that
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warrants them in light of other, better solutions." Added as `fewdualaxes`;
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year and URL queued.
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## Alternatives they give
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Side-by-side charts; indexed charts (with Knaflic's caveat that this fails when
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one series moves +10000% and the other +5%); prioritise-and-label; connected
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scatterplot. Our page's repentance already recommends the first two.
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