DATA to Insight

Capital in the 21st century

A widely discussed book is Thomas Piketty 2014 Capital in the Twenty-First Century (Harvard). A key datagraphic relates returns to capital r to the growth of world production g, and argues that the late 20th Century was a Golden Age when both were increasing together.

The specific datapoints are less important than the trends they are supposed to reveal. A design problem is that the time axis is in linear (equally spaced) steps but the time periods are not: interval end dates range from 500 down to 37 years. And without reading the text, I’m not sure about the last ‘data’ point made at the end of the 21st century!

My revision attempts to clarify this varying time scale using a logarithmic transformation:
      logpast = –log(year – 2200)
which uses an increasing time scale (more distance on the plot as we approach year 2200, where it is infinite). To clarify this unconventional approach I show centuries instead of the measurement dates. I don't show the actual data points, because the overall trends are more important. The distracting grid is removed, the curves are labeled, and the vertical (measurement) axis is at the right, which highlights recent (and presumably more reliable) measurements as well as future forecasts.