UNIVERSITY PARK, Pa. — Changes in the distribution of Pennsylvania's population — largely toward the state's southeastern quadrant — reflect challenges that policymakers need to address to promote and maintain statewide prosperity, suggests a new report compiled by economists in Penn State's College of Agricultural Sciences.

The report, Pennsylvania Population on the Move: 2000-17, graphically describes regional and county-level changes in population during the 2000-10 and 2010-17 time frames. These two periods roughly approximate business cycles influenced by the mild recession of 2001-02 and the "Great Recession" of 2007-09.

The report's findings mirror those of a companion report on employment trends released in 2018 that showed a significant contrast between southeastern Pennsylvania, which experienced mainly job growth from 2000 to 2017, and the rest of the state, with primarily job decline. This trend suggested the existence of "two Pennsylvanias," the economists said.

Although employment and population growth are almost certainly correlated, determining the reasons for these shifts is complex.

"People follow jobs, and jobs follow people," said co-author Theodore Fuller, development economist in the Department of Agricultural Economics, Sociology and Education. "But it's hard to establish cause and effect when you also consider migration in and out of the state and other economic and demographic factors."

In their latest report, the researchers used data from the U.S. Census Bureau, the American Community Survey, the Center for Rural Pennsylvania, and the U.S. Department of Commerce Bureau of Economic Analysis to analyze shifts in total population — and in several components of population — in these "two Pennsylvanias."

"Trends in total population can obscure changes in important components of population related to employment," explained co-author Theodore Alter, professor of agricultural, environmental, and regional economics. "So, in addition to total population, we looked at five components of population likely correlated with short-run employment change."

These components included net migration (residents moving to and from a locale), natural increase/decrease (difference between live births and deaths), potential workforce population (people aged 18 to 64 years), old-age dependency ratio (ratio of those 65 and older to those 18-64 years old), and median household income.

The data showed a wide disparity in population measures between the 15 counties designated as southeastern Pennsylvania — including the Philadelphia metropolitan statistical area — and the 52 counties in the western, central, northern and northeastern regions of the state.

For instance, southeastern Pennsylvania gained almost 450,000 residents from 2000 to 2010 and gained nearly 200,000 more between 2010 and 2017. The only other region to show increases in population during both time periods was central Pennsylvania, with gains of 26,631 and 657, respectively.

By comparison, western Pennsylvania, which the report defines as 19 western counties from Erie to the southern border and includes the Pittsburgh metropolitan statistical area, lost more than 100,000 residents in the first decade of the century and another 68,000 from 2010 to 2017.

Overall, 19 counties gained population during both time periods, including all 15 in the southeast. Twenty-nine counties lost population during both time periods. These gains and losses resulted in southeastern Pennsylvania's share of the total state population increasing from 52.6 percent in 2000 to 55.3 percent in 2017.

An examination of net migration patterns revealed that during 2000-09, net migration contributed to population increases in 31 counties, mostly in northeastern and southeastern Pennsylvania. After the Great Recession, only 20 counties saw increases in net migration from 2010 to 2016, nine of them in the southeast. An analysis of population gains due to natural increase showed similar trends, with the bulk of increases occurring in the southeastern region.

Meanwhile, the potential labor force — people between 18 and 64 years old — grew in 52 counties during 2000-10, including solid gains in all 15 southeastern counties. Between 2010 and 2016, however, the potential workforce increased in only 16 Pennsylvania counties, 11 of them in the southeast.

In 2000, the old-age dependency ratio — the ratio of over-65 population to potential workforce population —  was below 25 percent in 23 counties, including 11 counties in the southeast. By 2016, only seven counties had dependency ratios below 25 percent. During the same time frame, the number of counties with dependency ratios of 30 percent or higher rose from 17 to 38.

Southeastern Pennsylvania counties also came out ahead in annual median household income. In 2016, 20 counties had median household incomes above the state average of $61,000, including 14 of the 15 southeastern counties. At the same time, 45 of 52 counties outside of the southeast had median household incomes below the state average.

If these recent trends continue, the researchers noted, they suggest solid economic growth for southeastern Pennsylvania and widespread decline for much of the rest of the state.

"People may ask what it is about southeastern Pennsylvania that draws people," Alter said. "The dynamism, the opportunities, and the many diverse businesses and employers certainly are draws."

The question for policymakers is, what can state and local leaders do to make the prosperity of the '"two Pennsylvanias" a top statewide priority, said Tessa Sontheimer, report co-author and undergraduate research associate. "How can we maintain and strengthen the competitive position of the southeast region in a global economy while stopping and reversing the long-term, widespread decline in the rest of Pennsylvania?"

The report is available on the Penn State Center for Economic and Community Development website.