This report, by Fiscal Policy institute looks at the 25 largest major metropolitan areas - and finds that immigrants make significant contributions.

In metro Pittsburgh immigrants represent 3% of population and 4% of GDP, and in metro Philadelphia immigrants represent 9% of population and 10% of GDP.

Check out the Keystone Research Center's press release which highlights PA data.

File Attachment: 

ImmigrantsIn25MetroAreas_20091130.pdf