Affordability takes into account not only housing cost, but the ratio of median house price divided by gross annual median household income. This is a better indicator of affordability than housing price alone because it normalizes the housing prices by incorporating income, allowing comparison between cities.
The ratings of affordability are:
Severely Unaffordable – 5.1 & Over
Seriously Unaffordable – 4.1 to 5.0
Moderately Unaffordable – 3.1 to 4.0
Affordable – 3.0 & Under

The rating system is based on the “Median Multiple” described above, which is the agreed upon method of determining affordability and is widely used internationally, including international organizations. The fact that this method is widely agreed upon to be the best and it is used by large international organizations, it is safe to assume the data is “trustworthy.”

Affordability is a good measure of a city’s livability. If you can’t afford shelter, then livability will be highly compromised. Shelter is one of the most basic needs we have in life.