The majority of people living in Massachusetts' biggest cities are renters.

Renters make up about two-thirds of occupied housing units in the city of Boston, as well as in neighboring Cambridge and Somerville, and renters make up more than half of residents in all of Massachusetts’ 15 largest cities.

And the cost of rent has gone up in recent years — an overall increase of about 15 percent since 2011 in the commonwealth’s 15 largest cities. The increase has been much sharper in many communities. In Cambridge, gross rent has increased by about 23 percent, or nearly a quarter, since 2011; in Lynn, it’s increased by about 19 percent, or just less than one-fifth.

But rising rents only tell part of the story.

A WGBH News analysis of data collected by the U.S. Census shows that behind the seemingly straightforward fact of rising rents is a much more complicated picture. Our analysis found that between 2011 and 2017, the most recent period for which reliable data was available, the change in rent burden — rent measured as a percentage of household income — has varied drastically among Massachusetts’ largest cities.

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The reasons for these differences are complex, involving differing trends in property values and incomes, as well as demographic changes as an overall influx of new residents into Massachusetts cities reshapes local housing markets.

But the overall trend is clear: a dearth of affordable and family rental housing across the Greater Boston area is increasingly squeezing renters. In its most recent annual "Greater Boston Housing Report Card," The Boston Foundationfaulted suburban zoning lawsthat prevent the construction of multi-family rental housing as one of the chief drivers of this problem.

Our analysis found other patterns within this larger trend that further complicate the picture of rent burden across and within Massachusetts cities.

Among those findings: In many of the commonwealth’s least wealthy cities, residents have seen a sharp increase in the percentage of their income spent on rent. In several cities with booming economies — like Boston, Somerville and Cambridge — the rent burden has been relatively flat, and in some cases has actually decreased overall.

And those city-wide trends belie still more complicated differences within cities themselves, where changing rent burdens can vary drastically from neighborhood to neighborhood, painting a complex picture of winners and losers when it comes to housing affordability and uneven benefits from recent economic growth.

Rent Burden In Massachusetts Cities

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Among Massachusetts’ 15 largest cities, the average rent burden (the percentage of household income paid toward rent) was just over 30 percent in 2017, the most recent year for which U.S. Census data was available.

But there was significant difference between the lowest and highest rent burdens among those 15 cities — in many cases, though not all, corresponding to the relative wealth of those cities’ residents.

In Springfield, where the median household income is about $34,000 per year, renters paid a median 37 percent of household income toward rent.

At the other end of that spectrum, in Somerville, where median household income is about $67,000 — almost double that of Springfield — renters paid a median 26 percent of household income toward rent.

As Rents Rise, Changing Incomes Vary Widely Among Massachusetts Cities

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It seems to go without saying that rents are rising in Massachusetts cities — and, in terms of raw dollars, they are indeed rising across the board.

But in some of the commonwealth’s largest cities, rent as a proportion of household income is not rising. In fact, the overall rent burden in some Massachusetts cities has decreased in recent years.

In other cities, the opposite has been true: residents are, overall, paying more — often significantly more — of their households incomes toward rent.

The city of Lowell saw the greatest increase in rent burden among the commonwealth’s largest 15 cities between 2011 and 2017, with residents paying 12% more of their household incomes in rent in 2017 than in 2011. The cities of Springfield, Worcester and Newton also each saw significant increases in overall rent burden.

Conversely, the city of Somerville saw the greatest decrease in rent burden — overall, Somerville residents paid 7 percent less of their household incomes toward rent in 2017 than in 2011, followed by the cities of Lawrence, Brockton, Cambridge and New Bedford.

Within Boston, Highest Rent Burdens For Least Wealthy Neighborhoods

For many residents of greater Boston, it might seem counter-intuitive that average rent burdens have been level or even dropped in cities like Boston, Somerville and Cambridge.

That's because for many residents, the opposite has been true. A more detailed examination of data collected at the census tract level shows stark inequality in families' rent burden.

Reliable data for these smaller geographies is limited, and estimated margins of error are too large for reliable comparisons in most Massachusetts towns and cities.

But Boston, dense enough to provide reliable data, serves as a telling example of how widely rent burden can vary within a single community.

In Boston, families paying more than one-third of household income toward rent are concentrated in a few neighborhoods: Roxbury, Dorchester, Mattapan, Roslindale, parts of East Boston, Allston, Hyde Park, parts of West Roxbury and Jamaica Plain.

Meanwhile, renters in the city's wealthiest neighborhoods may be paying higher rents, but they are paying significantly less of their overall income toward rent.

Put another way: In Boston, It's easier for wealthy renters to rent in expensive neighborhoods than it is for less wealthy renters to rent in neighborhoods that would seem, on paper, to be less expensive to live in.

The greatest concentration of these rent-burdened census tracts are in neighborhoods that have been traditionally working-class and low-income, and which have seen rapid gentrification in recent years — especially the Roxbury-Dorchester-Mattapan corridor.

The data bolsters concerns by residents of these neighborhoods, their elected officials and housing advocacy groups, that the city's less-wealthy renters are under increasing strain when it comes to being able to afford rent.

High Rent Burden Areas Of Boston

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Orange represents Boston census tracts where the average household in 2017 spent one-third to one-half of income on rent. Red represents census tracts where the average household spent more than one-half of income on rent.
Isaiah Thompson WGBH News

Meanwhile, there are a handful of census tracts in Boston in which residents, on average, are paying much less of their overall income toward rent — less than one-fourth — even though housing prices in those neighborhoods are, in raw dollars, significantly higher.

The greatest concentration of "low-burden" renters is in census tracts in downtown Boston, South Boston, the South End, Back Bay and Charlestown.

In these wealthier neighborhoods, renters are paying higher rents in terms of dollars; but compared to household incomes, those families are paying significantly less than their neighbors in less affluent parts of the city.

Low Rent Burden Areas Of Boston

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Blue represents census tracts where the average household in 2017 spent less than one-quarter of income on rent.
Isaiah Thompson WGBH News