Massachusetts continued to record more births than deaths from July 2021 to July 2022 even though the state’s total population shrunk in that span, suggesting that residents decamping to other locales is the primary driver of a trend that has ramped up pressure on policymakers.

The Bay State was ahead of the pack in terms of population growth from 2010 to 2020, surpassing the national median. It was also the fastest-growing state that decade among its contiguous neighbors, according to U.S. Census data presented at a Massachusetts Taxpayers Foundation forum.

That flipped in the years since the COVID-19 pandemic hit, triggering a surge of what Pew Trusts analyst Joanna Biernacka-Lievestro called “scary headlines.”

“Is it true that basically everyone in Massachusetts is just packing up and heading to sunny Florida? Well, not quite, but there is something to it,” Biernacka-Lievestro said.

Eighteen states experienced population declines between July 2021 and July 2022, she said. In 12 of those, including Massachusetts, the drop was driven by outmigration, meaning enough people moved away to outpace population growth from new arrivals and births.

More people came to Massachusetts than left it each year from 2008 to 2018, according to data Biernacka-Lievestro presented, and since then, the trend has accelerated in the opposite direction.

The emerging dynamic has become a key point in debate about a range of public policy topics, including housing costs, transportation systems, the state’s tax code and access to child care.

Tricia Canavan, CEO of the Springfield-based Tech Foundry, said the problem is “even more urgent” in western Massachusetts, which continues to lose younger residents early in their careers to other states.

“What does this mean in 20 years for the state?” Canavan said, warning that Massachusetts might struggle to stay “competitive” if its workforce continues to shrink.

Beacon Hill aimed to stem the tide by enacting a roughly $1 billion tax relief package that supporters say will make Massachusetts more affordable and competitive. Gov. Maura Healey also filed a policy-heavy housing bond bill last week that she pitched as a way to boost much-needed production and help residents find affordable homes.

Luc Schuster, executive director of the Boston Indicators research center, said the data “just jumps off the page how much housing has to be a central driver of the domestic outmigration we’re seeing.”

“It’s a weird dynamic because we’re starting to see an acceleration of people moving out of Greater Boston, so in a sense, that’s demand going down, but it’s as housing costs continue to rise dramatically,” he said. “To me, there’s just a lot going on here, but I can’t help but think about how much more prosperous we could be if we fixed our housing problem.”

Schuster previewed findings from the “2023 Housing Report Card” his group plans to release next month, which indicated similar population losses specifically within the Greater Boston region.

“The net domestic outmigration [from Greater Boston] has been negative for almost a decade now, and it’s accelerated in the last two years, so that’s really disturbing,” Schuster said.

Research from Boston Indicators found that the flow is not limited to one subset of the population ladder, either: low-, middle- and high-income residents are each leaving the area at an accelerating rate, Schuster said.

Massachusetts Taxpayers Foundation President Doug Howgate, whose group was among the many voices calling for business-friendly tax relief measures to make the state a more attractive hub, warned of a potent “one-two” punch.

“It’s concerning when you see that increased decline in higher-income folks, because that is a key part of our economy. How do we make sure that we are competitive for those folks to stay here?” he said. “And at the same time, what you absolutely don’t want is higher-income folks leaving because they don’t want to be here, and lower-income folks can’t afford to be here, either.”

A new income surtax devised and advanced by Democrats and approved by voters is newly pulling more than $1 billion a year from the state’s highest-income households. Supporters say the money will help make needed investments in transportation and education while opponents of the tax have warned it may drive some people and their wealth out of Massachusetts to states with lower taxes.