Average test score in mathematics and science vs. GDP per capita, 2016

Shown on the x-axis are Hanushek and Woessmann's combination of scores from international student achievement tests. The scores are standardized to the PISA
test scale, so that the OECD countries have a mean of 500 and a standard deviation of 100. The test scores are here plotted against GDP per capita in 2016, but the
test scores are not from a particular year, and instead are the average of all standardized math and science test scores each country participated in.