[EDIT: OK, Whit just asked "the world?" incredulously, and I double-checked the article. Turns out the report covers housing markets in Australia, Canada, Ireland, New Zealand, the United Kingdom and the United States. So, not the world.]
Via Apartment Therapy SF:
Every year for the past six years, an organization called the Frontier Centre for Public Policy conducts something called the Demographia International Housing Affordability Survey. The survey gathers information about housing costs, then compares this data against median household incomes.San Francisco is tied with New York (both have a score of 7.0). But we're more affordable than Vancouver (9.3)! Las Vegas has a score of 2.4 (ranked 31 most affordable). Maybe now my dad will stop bugging me to try and buy a house around here.
The report's authors, Wendell Cox and Hugh Pavletich, who based their findings on 2009 third-quarter data, said that to be considered affordable, housing prices have to have a Median Multiple of 3.0 or less – or, in other words, the price of the average home must be equivalent to no more than three years’ household income for an average family in that area.
The Median Multiple scale progresses upward from there: Moderately Unaffordable is 3.1 to 4.0; Seriously Unaffordable is 4.1 to 5.0; and Severely Unaffordable is 5.1 and higher.