Paul Krugman questions whether there is an existence of positive relationship between equality and growth. He rightly cautions those on the left against being too quick to accept the existence of such a relationship.
He uses a simple graph showing the relationship between inequality and growth per working age person in the years 1985 to 2007. His takeaway is that there is not much of a positive relationship, but there clearly is no negative relationship between equality and growth. In other words, the people who argue that we need to have more inequality to support stronger growth have a hard case to make using this simple comparison.
I would suggest taking the analysis one step further. One big difference between countries over this period is the extent to which they opted to take the benefits from growth in more leisure time. There are large differences in the decline in the length of the average work year across countries.
Using the OECD data (which is not perfect for international comparisons) we find that relatively equal France saw a decline in average work hours of 10.2 percent over this period. Denmark had a decline of 5.3 percent, and West Germany had a drop of 15.9 percent. These would translate into annual increases in GDP per potential work hour of 0.5, 0.2, and 0.8 percentage points, respectively.
By contrast, in the relatively unequal U.K. the drop in average hours was 4.7 percent, in Canada 3.1 percent, and in the U.S. 2.2 percent. These translates in gains in annual GDP per potential hour worked of 0.2, 0.1, and 0.1 percentage points, respectively.
Would looking at GDP per potential hour worked strengthen the positive correlation between equality and growth? I don't have time to check that one just now, but a quick eyeballing of the data suggests that it is possible. This still would not be conclusive evidence that equality is good for growth, but it would be interesting. And, it is an important reminder that there is nothing wrong with taking the benefits of higher productivity in the form of leisure rather than income. The planet will thank you for it.