When a Place Looks More Affordable

This chapter diagnoses a specific warning sign in renter-affordability data: the lowest-rent places saw rapid rent growth, yet their area median rent-to-income ratio rose less than the ratios of several higher-rent groups. The question is whether that smaller increase means renters in those places became safer, or whether the people being averaged changed. The useful judgment is to treat an improving area statistic as a composition-sensitive hypothesis until the experience of incumbent renters can be separated from the experience of new arrivals.

The symptom: slower ratio growth alongside faster rent growth

The Federal Reserve study reports that the lowest pre-pandemic rent quartile saw the smallest increase in its area median rent-to-income ratio from 2019 to 2022. Its ratio rose from 30.3 to 30.8 percent, an increase of 0.6 percentage points. The second quartile rose by 2.5 points, the third by 2.1 points, and the fourth by 1.5 points.

At first glance, this looks like a favorable result for the cheapest places. A smaller increase in rent relative to income can sound like evidence that affordability held up better there. But the same study finds that lower-rent places experienced rapid rent growth, and that average rent spending rose in every rent quartile. The lowest-rent quartile went from an average of $775 in 2019 to $926 in 2022. Its smaller ratio increase therefore cannot be read as a simple report that rent pressure was weaker.

The apparent puzzle comes from combining two different movements. The numerator of an area rent-to-income ratio is related to local rent. The denominator is related to the income of the households counted in the area. If rents rise but the population’s measured income rises as well, the ratio can increase only slightly. That arithmetic is not a trick or a data error. It is a reminder that an area ratio records the joint result of prices and population composition.

A ratio can therefore answer the question, “How did rent compare with the income of the people counted in this place at each observation?” It cannot automatically answer, “Did the renter who was already here become more able to pay?” Those questions overlap when the population is stable, but they separate when a place is receiving or losing households with different incomes.

Three simplified comparisons make the problem visible. If local rents rise while the same residents’ incomes stay unchanged, the ratio should rise and the interpretation is comparatively direct. If local rents stay unchanged while higher-income residents move in, the area ratio can fall even though incumbent renters did not receive a rent reduction. If rents rise and higher-income residents move in at the same time, the ratio can rise a little, stay flat, or fall depending on the size of the two changes. The observed ratio alone does not reveal which of these cases produced it.

The Federal Reserve result is important because the geography makes the third case plausible, not because it proves a single decomposition.