Economic analyst Hank Fishkind has been reviewing immigration from an economic perspective, which, at its basic level, he says boils down to its role in boosting U.S. GDP, or gross domestic product.

According to Fishkind, growth of GDP depends on just two things: an increase in the number of hours worked, and a rise in output per man-hour that we call “productivity.”

And Fishkind tells 90.7’s Nicole Darden Creston there’s an important relationship between population growth and productivity.