Maria Sanchez-Lopez and her husband just rented a house in Randolph, a three-bedroom home with room for their two twentysomething children and a big backyard. It's a place they never would have been able to afford closer to their jobs in the city — despite their combined salary of more than $90,000 a year from her job as a program administrator for the state and his work as a postdoc biotech researcher.
"I don't consider myself middle class, I really don't," said Sanchez-Lopez, 47, a Roxbury native who spent a several-year odyssey in search of an affordable place to live, moving from the South End to West Roxbury to Chelsea before landing in Randolph this summer. "I thought I was, at one point. But I realized I'm not."
Sanchez-Lopez's family is among the many that make a decent living but are getting edged out of Boston as housing prices and rents soar. The share of moderate-income Boston households fell by 3 percentage points, to 26 percent, from 2000 to 2013, according to an analysis of the most recent census data done for the Globe by the Metropolitan Area Planning Council, a regional planning agency.
The numbers confirm a decline in the share of middle-income working families in Boston that's been happening since 1990, even as the percentage of lower- and higher-income families increased, according to a recent Northeastern University study of two decades of census data.
The drop comes as the population of the city itself has slowly increased in recent years to about 656,000.
The studies did not include data on what exactly is happening to these families, but to Barry Bluestone of Northeastern University the cause is clear.
"Working families are just moving farther and farther away from the central city," said Bluestone, director of the Dukakis Center for Urban and Regional Policy, which analyzed in-depth census data compiled every 10 years to track the pace and scope of the decline.
This loss of middle-income families can have a profound effect on workers and the city, economists and housing advocates say. If more people are living farther from their jobs in Boston, it means longer and costlier commutes — and higher prices in outlying communities as demand increases.
It also means that Boston's neighborhoods have increasingly become home to the rich or the poor, and to a rising number of college students, with fewer families in between.
More than half of the city's leases start or expire in early September, according to the online rental database Rental Beast, throwing that demographic shift into sharp relief at this time of year.
"I worry about that missing middle," Bluestone said. "If this continues, we may be creating a new working-class nomad population."
From 1990 to 2010, the share of families earning between two and five times the poverty level (a family of four making $49,000 to $121,000 a year) dropped by nearly 8 percentage points, from almost 43 percent to just over 35 percent, according to the Dukakis Center's analysis.
In some cases, the loss of such a family in Boston might not mean that they actually left. Instead, a job loss may have forced them into a lower income bracket. Indeed, the city's share of lower-income families has risen slightly over the past two decades, according to Northeastern. And there are always those who leave because they want to or are following employment outside of Boston.
But some people have no choice, including former low-income families who work their way up and no longer qualify for the subsidies that allowed them to stay, advocates say.
"They have become middle-class families, and they can no longer afford to live in the city," said Vanessa Calderon-Rosado, chief executive of the South End affordable housing nonprofit Inquilinos Boricuas en Acción.
Several municipalities near Boston have also seen a decline in moderate-income households, including Cambridge, Quincy, and Lexington. At the same time, some slightly farther out — such as Holbrook, Marlborough, and Peabody — have seen these populations rise in recent years, according to the Metropolitan Area Planning Council.
Marie Bain may soon be among those looking for a cheaper place outside Boston. Bain, who lives with her two adult sons, lost the home she owned in Hyde Park after she took time off from her job as a nursing assistant, for which she makes $48,000 a year, to care for an adult son who later died of brain cancer. Now she is looking as far away as Norwood and Brockton to find a place in her price range of $1,500 a month. But she works nights on a busy surgical floor at a Boston hospital and is sometimes so tired when she leaves that she has to pull over on the side of the road to rest.
"By the time I get to Brockton," she said, "I might fall asleep behind the wheel."
Renters are being hit particularly hard. Median rents in Boston have climbed nearly 50 percent since 2005, to $2,200 a month, according to city data, while wages have stagnated. In all, Boston rents are increasing at five times the rate of income, according to the city.
Complicating the problem, real estate developers are scooping up multifamily buildings in places like Dorchester and East Boston, fixing them up to attract higher-end renters and sometimes evicting tenants in the process, housing advocates say.
Among their best customers? Students and young professionals, who split the rent with roommates, squeezing out families who can't afford the new-and-improved units.
City Life/Vida Urbana, a Jamaica Plain community group, is pushing the city to adopt more protections for tenants as an increasing number are displaced, particularly in the past few years.
Among those affected is Orlando Espinal, who is facing eviction after his Roslindale apartment building was sold this year and the new owner ordered the renters out.
Espinal, 54, makes nearly $70,000 a year helping people with disabilities find work, but the only suitable places he can afford are far outside the city, which would mean yanking his teenage son out of Fenway High School.
This outward pressure could also be contributing to climbing rents in the suburbs. In the past year, average rents have risen almost 10 percent in towns south of Boston — twice as fast as in the region as a whole — according to the real estate data firm Axiometrics.
If workers can't afford to live in Boston, it will make the city less attractive to employers, said Sheila Dillon, director of Boston's Department of Neighborhood Development. The city is trying to alleviate what it has called the "unprecedented difficulties" middle-income families are facing in finding housing, including pushing for the building of more than 26,000 units of housing for lower- to middle-income families and new dormitories to get more students out of working-class neighborhoods.
Yet a fundamental problem remains, Dillon acknowledged: "We don't have a solution for landlords coming in and saying, 'I'm going to triple the rent.' "