Confusion is not limited to complex dataviz
Jul 07, 2016
This chart looks simple and harmless but I find it disarming.
I usually love the cheeky titles in the Economist but this title is very destructive to the data visualization. The chart has nothing to do with credit scores. In fact, credit scoring is associated with consumers while countries have credit ratings.
Also, I am not a fan of the Economist way of labeling negative axes. The negative sign situated between 0 and 1 looks like a stray hyphen that the editor missed.
A line chart would have brought out the pattern more sharply:
The pairing of columns in the original chart signals that readers should compare GDP growth to population growth. A good point, since GDP scales with population.
Controlling for population size can be accomplished by the per-capita GDP growth rate.
The last three years are clearly different. By this metric, different in a good way.
This chart creates a problem for the journalist. The article is about the deal to "save" Puerto Rico which some has criticized as colonial. Presumably, the territory has been in dire straits. There are plenty of metrics to illustrate this point but GDP growth is not one of them.
I broadly agree with your points about the original chart not being clear.
However, if the article the chart was attached to was about Puerto Rico's stock of outstanding debt, it actually can make sense to show population and GDP instead of GDP per capita, as total GDP and population would affect how much revenue can be raised.
Posted by: Michael | Jul 07, 2016 at 10:40 PM
Michael: actually, if GDP is of interest, both charts are necessary to paint the picture. One gives the insight that the per-capita GDP nominally appears to be improving (I didn't check if these are in real dollars) but that metric paints a misleading picture since the improvement is driven by a decline in population. However, the point of the post is that this chart does not work in the context of the Puerto Rican story at the moment.
Posted by: Kaiser | Jul 08, 2016 at 11:38 AM
While I agree on the importance of showing GDP-per-capita, I have to admit I am not a big fan of using line charts to show values which are derivatives (i.e. growth rates): A line chart always projects a downward or upward "trajectory" in my mind, which in case of derivatives can often confuse. A growth rate with an upward sloping line at least in my mind projects an image of "growing", which is misled of a negative rate is just getting less negative (but the original variable is still shrinking)...
Posted by: Alex | Jul 12, 2016 at 09:44 AM