Section 4 looks at specific challenges that could arise during the implementation of these policies and how best to address them. Income disparities have risen to unprecedented levels in some countries over the past three decades, with the richest 10% in the OECD area earning almost ten times more than the poorest 10%. Wealth is even more concentrated than income: in 2012, the richest 10% controlled half of all total household wealth, while the poorest 40% held only 3% of the total across 18 OECD countries3 (OECD, 2015a).