Statistical corruption in Beijing's air quality data has likely ended in 2012
This research documents changes in likely misreporting in official air quality data from Beijing for the years 2008 to 2013. It is shown that, consistent with prior research, the official Chinese data report suspiciously few observations that exceed the politically important Blue Sky Day threshold and an excess of observations just below that threshold. Similar data, measured by the US Embassy in Beijing, do not show this irregularity. To document likely misreporting, this analysis compares the air quality measurements to Benford’s Law, a statistical regularity known to fit air pollution data. I find that the Chinese data fit Benford’s Law poorly until a change in air quality measurements at the end of 2012. From 2013 onwards, the Chinese data fit Benford’s Law closely. The US Embassy data, by contrast, exhibit no variation over time in the fit with Benford’s Law, implying that the underlying pollution processes remain unchanged. These findings suggest that misreporting of air quality data for Beijing has likely ended in 2012.