More political graphics

This one is from Young Labour, and as with the previous examples it was retweeted  into my Twitter feed. It’s a useful contrast to the previous, since it’s misleading only in the standard ways you expect from political graphs; it’s not an outright distortion.

Good points: there is a reasonable data range, which is important for time-series comparisons. The vertical axis is labelled, and the labels match the quantities they are supposed to match.

From an economic point of view, there’s a problem.  The increase in debt under John Key’s government was largely due to the Great Recession.  Labour, one would hope, would also have run deficits during a major recession — that’s what you do — and there’s no way that the Great Recession can be blamed on the NZ National Party.  So, as is often the case, there are important confounding factors in the time series.  The numbers are right, but they don’t really support the obvious causal conclusion.

The graphical criticism: the vertical axis begins at 5% rather than at 0.  While for line graphs there are a range of  views about when zero needs to be included and how, there really aren’t for bar graphs. The area of the bar is supposed to convey information.

If you look up the data source, you find that it truncates the vertical axis in exactly the same way, which is presumably the reason (though hardly an excuse)

Redrawing, we can see what the graph should have looked like; I think the distorting effect is real but relatively small, especially for the last decade (which, again, not an excuse)

And, in fact, using the wonders of PowerPoint and image transparency, I found that the Young Labour graphic and the one from the TradingEconomics.com can be exactly superimposed — which I suppose argues against the vertical distortion being deliberate.

There’s just one more thing.

You will have noticed, perhaps, that my redrawn graphic has two red bars on the right-hand end, but Young Labour’s has three, with the last two at about the same height. If I hadn’t gone to the effort of superimposing the two versions I would have thought it was probably due to different divisions of the time axis or something.  But it’s not. An extra bar has been added. That’s a bit suspicious.

Or, it would be if it weren’t about the same height as the previous bar.  It turns out, if you go to the Treasury’s  Interim Financial Statements for the four months ending 2019-10-31, you find a figure of 20.2%, which seems to be the height for the last bar. On the one hand, that’s not precisely comparable to the rest of the graph; on the other hand, it’s probably the best that could be done, and shows a reasonable degree of care.