Cities around the world, from New York to London to Stockholm to Sydney, are struggling to solve growing affordable housing crises.

Acute shortages are persisting despite millions of dollars invested and hundreds of thousands of units built. Some countries have focused on solutions promoting unshackled free markets while others have turned more to rent control and subsidies.

But no approach has solved the crises and most have other negative ripple effects.

Across 32 major cities around the world, real home prices on average grew 24% over the last five years, while average real income grew by only 8% over the same period, according to Knight Frank, a London-based real-estate consulting firm.

Economists say it is striking that affordability has worsened even during a period of global prosperity over the last six years. But income growth has been unable to keep pace with a rapid run-up in home prices.