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The case against dual axis charts (and what to use instead) (2018)
We believe that charts with two different y-axes make it hard for most people to intuitively make right statements about two data series.
In fact, of these four use cases, we think that only the last dual axis chart can be used without any doubt, since it only uses the second Y-axis to show an alternative scale and not a second data series. Here’s the problem in a nutshell: The scales of dual axis charts are arbitrary and can therefore (deliberately) mislead readers about the relationship between the two data series. Indeed, this solution won’t work well for most data (including ours), but can be a great alternative for dual axis charts that present absolute and relative numbers of the same measure.
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