1 Housing Inequality: Concepts and Measures

Dimensions of housing inequality

Housing inequality involves unequal access to housing that is affordable, stable, and adequate, as well as unequal access to neighborhoods with different opportunities. Housing affordability, Residential segregation, and Homelessness describe distinct parts of this system. No single measure captures the whole problem.

Measuring housing affordability

Housing is generally considered affordable when a household can pay for it without sacrificing too much income needed for other essentials. A widely used benchmark treats housing costs above $30\%$ of household income as a cost burden; costs above $50\%$ are commonly described as a severe cost burden. These thresholds help compare households and places, but they are guidelines, not a complete measure of whether a household can meet its needs.

The basic housing cost-to-income ratio is:

For renters, housing costs typically include rent and utilities. For homeowners, measures may include mortgage payments, property taxes, insurance, utilities, and applicable fees. For example, a household earning $\$2{,}000$ per month and spending $\$800$ on housing has a ratio of $40\%$, so it is cost-burdened under the $30\%$ benchmark.

An income-based approach compares housing costs with what households at particular income levels can afford. It highlights affordable-housing gaps: the difference between the number of homes affordable to a given income group and the number of households in that group. This approach is especially useful because a modest rent in an expensive market may still be out of reach for a very low-income household.

What affordability measures leave out

The $30\%$ measure has important limits. It does not show how much money remains after housing costs, whether a home is safe and adequate, or whether the household can reach jobs and services. A low-income household may have very little left even when its ratio is below $30\%$, while a higher-income household may spend more than $30\%$ without facing the same hardship. Researchers therefore also examine residual income, housing quality, and location.

Patterns of residential segregation

Residential segregation describes how groups—often groups defined by race or ethnicity—are distributed across neighborhoods within a larger area. It can result from multiple forces, including past and present housing policies, discrimination, unequal access to credit and housing, and land-use decisions. Segregation is not a single condition captured by one statistic: different measures describe different spatial patterns.

Evenness and exposure

Evenness describes how similarly groups are distributed among neighborhoods. The dissimilarity index is a widely used measure of evenness. It ranges from $0$ to $1$, or from $0$ to $100$; a value of $0$ indicates an even distribution, and $1$ indicates complete separation. Conceptually, it estimates the share of one group that would need to move for each neighborhood to match the larger area's group composition.

Exposure concerns the likelihood that members of different groups share a neighborhood. The interaction index estimates potential contact between groups, while the isolation index estimates a group's exposure to members of its own group.

Other spatial dimensions

Concentration describes how much physical space a group occupies. Centralization describes how near it is to the urban center, and clustering describes how strongly its neighborhoods adjoin one another.

Two cities could have similar dissimilarity scores but different exposure if the groups differ in population size. A dissimilarity score describes uneven distribution; by itself, it does not tell us how much contact residents are likely to have or whether neighborhoods have equal resources. Results also depend on the boundaries used to define neighborhoods and the larger area being studied.

Understanding homelessness measures

Homelessness means lacking a stable place to live, but definitions vary by program and measurement system. In HUD's point-in-time (PIT) counts, the count focuses on people staying in emergency shelters, transitional housing, and Safe Havens, as well as people sleeping outside or in other places not meant for human habitation. It is a one-night snapshot, not a count of everyone who experiences homelessness over a year.

The two principal PIT categories are:

• Sheltered homelessness: Staying in an emergency shelter, transitional housing, or a Safe Haven.

• Unsheltered homelessness: Staying outside or in a place not intended for regular sleeping, such as a vehicle or an abandoned building.

PIT counts help estimate the scale and characteristics of homelessness at a particular time. Because they are snapshots and depend on local counting methods, they do not capture every episode or every form of housing instability. People temporarily staying with friends or relatives, for example, may face serious housing insecurity but may not be included in the same PIT categories.

How the dimensions interact

Affordability, segregation, and homelessness are distinct, but they interact. High housing costs relative to income can leave households with little capacity to manage a rent increase, job loss, medical expense, or another shock. Eviction or displacement can lead to frequent moves, doubling up, or homelessness. A shortage of housing affordable to people with very low incomes can increase these risks, while rental assistance and other supports can help households remain housed.

Segregation shapes who can access which housing and neighborhoods. When affordable homes are concentrated in a limited set of places, households may have fewer choices about location and less access to jobs, schools, transit, and services. Historical and ongoing discrimination can also affect access to housing and opportunity. These patterns can reinforce unequal incomes and wealth, influencing what housing households can afford and how vulnerable they are to displacement or homelessness.

A complementary analysis asks three questions:

1. Can households afford adequate housing? Examine cost burdens, severe burdens, income-based affordability gaps, and residual income.

2. Who lives where, and what opportunities are available there? Examine segregation across relevant spatial dimensions, along with neighborhood access to jobs, services, and other resources.

3. Who lacks stable housing, and how is that measured? Distinguish sheltered from unsheltered homelessness and identify whether the evidence is a one-night count or a longer-period measure.

Together, these measures show that housing inequality concerns more than rent or home prices alone. It also concerns the ability to obtain and keep a suitable home, the choices households have among neighborhoods, and the consequences when stable housing is unavailable.