The other major factor is the measurement of housing costs.
Some organization and agencies consider the cost of purchasing a single-family home; others look exclusively at the cost of renting an apartment.
Many U.S. studies, for example, focus primarily on the median cost of renting a two-bedroom apartment in a large apartment complex for a new tenant. These studies often lump together luxury apartments and slums, as well as desirable and undesirable neighborhoods. While this practice is known to distort the true costs, it is difficult to provide accurate information for the wide variety of situations without the report being unwieldy.
Normally, only legal, permitted, separate housing is considered when calculating the cost of housing. The low rent costs for a room in a single family home, or an illegal garage conversion, or a college dormitory are generally excluded from the calculation, no matter how many people in an area live in such situations. Because of this study methodology, median housing costs tend to be slightly inflated.
Costs are generally considered on a cash (not accrual) basis. Thus a person making the last payment on a large home mortgage might live in officially unaffordable housing one month, and very affordable housing the following month, when the mortgage is paid off. This distortion can be significant in areas where real estate costs are high, even if incomes are similarly high, because a high income allows a higher proportion of the income to be dedicated towards buying an expensive home without endangering the household's ability to buy food or other basic necessities.
Furthermore, the absolute availability of housing is not generally considered in the calculation of affordable housing. In a depressed or sparsely settled rural area, for example, the predicted price of the canonical median two-bedroom apartment may be quite easily affordable even to a minimum-wage worker – if only any apartments had ever been built.
An article in the 2007 issue of Atlantic Monthly reported on a study of the cost of obtaining the "right to build" (i.e. a building permit, red tape, bureaucracy, etc.) in different U.S. cities. The study was conducted by Harvard economists Edward Glaeser and Kristina Tobio. According to the chart accompanying the article, the cost of obtaining the "right to build" adds approximately $600,000 to the cost of each new house that is built in San Francisco. [1]