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Revenue is definitely discrete; though it doesn't say it on that chart, I would assume given the context that the revenue units is "million dollars per month". Since market share is probably calculated from revenue, you could probably argue that one either way.


The double axis graph would be most effective as a scatterplot (revenue vs market share, with each data point labeled by its month). Despite being Tufte's former student, she doesn't seem to have taken on board his observation that the media overwhelmingly prefers time series data even when a single bivariate plot is more illuminating.

Nick: just because revenue is reported monthly doesn't make it "definitely discrete". The revenue is being earned continuously during those months, and market share also changes continuously. Binning into conveniently-sized time bins doesn't itself convert the underlying data from being continuous into discrete.

Chris Mills

For me the problem is that you have to chart what you have, not what you want to have.

If Wong had monthly revenue and market share numbers to work with rather than more fine-grained readings, the chart above would be perfectly appropriate in my opinion. The choice is not a comment on the nature of the underlying data, it might just be an honest representation of the available data.

Am I missing something?


Leaving aside the issue of whether the type of graph is appropriate, I really like how it looks.

I thumbed through a copy of the book a few weeks ago. I found a rule or two I didn't agree with, but I might buy it just because of how much I like the style of the graphs: simple, spare, compact, and clear.

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