How should the productivity of research universities be measured? This task is difficult but important. The recent Research Excellence Framework in the UK, which was based on peer review, suggests that there has been a marked improvement in UK academic research in economics and in many other subjects. But is it possible to design an objective check on, and measure of, a nation's 'world-leading research'? Following a variant of a method developed in Oswald (2010), I examine citations data on 450 genuinely world-leading journal articles over the Research Excellence Framework period 2008-2014. The UK produced 54 of these articles, namely, 12%. This compares to 45 articles, namely 10%, using the same methodology over the Research Assessment Exercise period 2001-2008. I conclude that it is possible to produce an objective measure of world-leading research, and that UK economics did show a small improvement.