I took some time to do something totally crazy - like,
read the report - and while I ain't no international economist of mystery a few things stood out to me. According to the report:
Education does not improve economic growth. Throw heaps of money at education, whatever, doesn't make a difference.
Investment does not improve economic growth. Whatever, doesn't make a difference.
Inequality between the ninth and tenth deciles (high earners at the top of the scale) and the average income has no effect whatsoever on growth. Say it with me now, according to this report a huge inequality between the super-rich and the average earner has no impact on economic growth.
Inequality between the fourth decile (slightly-below average) income and the average income has a huge impact on growth. So the biggest thing you can do to improve economic growth is to tax the average earner more and lift the slightly-below-average earners a little bit.
And regarding the conclusion that everyone so excitedly jumped on after reading nothing but a badly-written headline in a news article: again, I ain't no economist, but it seems to me after reading the report that report's focus on New Zealand in the 80s and early 90s could lead to a completely reversed conclusion: that slow economic growth such as that experienced by NZ in that time negatively impacted equality. Not the other way around.