This link to the Harvard paper is in the article:

http://www.hks.harvard.edu/pepg/PDF/Papers/PEPG14-01_NotJust.pdf

This is the cut sheet on the USA from the OECD website:

http://www.oecd.org/unitedstates/PISA-2012-results-US.pdf

This is the PISA 12 page from the US Dept of Ed:

http://nces.ed.gov/surveys/pisa/pisa2012/index.asp

...pronounced like the long vowel and first letter of the alphabet...