The report covers roughly 1 billion people if you take the working population of the 33 countries involved. At a sample of 215942 the margin of error is fracti

The report covers roughly 1 billion people if you take the working population of the 33 countries involved. At a sample of 215942 the margin of error is fractions of a percent. But, what this doesn't account for is that in the original report (http://www.oecd-ilibrary.org/education/skills-matter_9789264258051-en http://www.oecd-ilibrary.org/education/skills-matter_9789264...) you do see a significant variance in the distribution of skills based on: -Country -Age -Income Example: In Japan, only 4.3% of adults are at a "Level 1" where as in Indonesia it is 37.2% which is to be expected when Indonesia is the bottom of the ladder in GDP Per Capita (http://www.keepeek.com/Digital-Asset-Management/oecd/education/skills-matter/per-capita-gdp-usd_9789264258051-graph7-en#page1 http://www.keepeek.com/Digital-Asset-Management/oecd/educati...) and in literacy scores (http://www.keepeek.com/Digital-Asset-Management/oecd/education/skills-matter/literacy-proficiency-by-educational-attainment_9789264258051-graph3-en#page3 http://www.keepeek.com/Digital-Asset-Management/oecd/educati...). While this report says it takes the 'average cross the OECD countries' it's not clear on which factors were weighted or adjusted. The information isn't wrong - it's just worth taking it with a grain of salt depending on how you are using the information. That said the US market for example lines up very close to the average, which is still staggering.