John Jerrim. 
A version of this blogpost also appears on the Centre for Education Economics website.
The OECD’s PISA study compares the science, reading and mathematics skills of 15-year-olds across countries, with the results closely watched by journalists, public policymakers and the general public from across the world.
It’s conducted every three years, and particular attention is now being paid to how the PISA scores of each country are changing over time. For instance, are the academic skills of young people in some countries improving, while in others they are in relative decline?
Of course, to answer such questions robustly, fair and comparable measures (more…)