The Pew Charitable Trusts' report found that more people still are leaving the city than are arriving, which was the case in each of the 16 years, from 1993 to 2008, that researchers examined.
However, the "net outflow" from Philadelphia to the suburbs and elsewhere - the number of people leaving minus the number of new arrivals - has dropped from a peak of 20,284 in 1995 to 9,846 in 2008.
"These changes in migration patterns are significant, and they have gone largely unnoticed," said Larry Eichel, project director of Pew's Philadelphia Research Initiative and the report's author. The findings support recent census estimates indicating that Philadelphia's population has risen slightly over the past 10 years, he said.
According to the report, the number of people moving to Philadelphia rose 33 percent in the time span studied, from 31,837 in 1993 to 42,250 in 2008. Meanwhile, the number of people moving away grew but less rapidly, from 47,921 in 1993 to 52,096 in 2008.
The researchers said that while the economic downturn may have partly helped big cities like Philadelphia because it became harder for people to relocate, the overall trends were happening before the recession began.
In 2008, the net outflow from Philadelphia to bordering Bucks, Chester, Delaware and Montgomery counties was 7,352 people - lower than in any of the previous years studied and down 42 percent from the peak of 12,595 in 1999.
The number of people leaving Philadelphia for its three closest southern New Jersey counties has "slowed to a trickle," the report said. After a peak net outflow of 4,029 in 2002, the number dropped to 1,031 by 2008 - the lowest in the period studied and the year that had the most movement into the city from those counties.
The figures also seem to support anecdotal evidence that Philadelphia has become home to New Yorkers looking for a more affordable place to live.
Migration from New York City to Philadelphia more than doubled during the period studied, from 1,332 in 1993 to 3,100 in 2008. However, in the past few years, larger numbers of people have left Philadelphia for New York and reduced the overall New York-to-Philadelphia increase to just 212 people by 2008, the most recent year statistics were available.
The report used Internal Revenue Service data on year-to-year address changes by tax filers.