# The housing policy matchmaker

**Population change**

Population change is measured as a growth rate between 2009 and 2019. The denominator is the midpoint between the two years, rather than the base year, because this metric reduces the probability of large outlier values for small-population counties.

**Housing value-to-income**

Housing value-to-income ratios are defined as below:

Affordability tiers for home value-to-income ratio assume that most homebuyers can afford to purchase a home approximately three times their annual income, while paying no more than 30% of their income on monthly costs (mortgage principal and interest, property taxes, and insurance). The relationship between housing values and monthly housing costs depends on a variety of factors, including prevailing mortgage interest rates, down payment amounts, and local property tax rates.

**Income needed to pay median rent**

The minimum income needed to pay median rent is calculated below, assuming that households should spend no more than 30% of their income on rent: