MEXICO CITY – The number of migrants crossing illegally into the United States from Mexico appears to have risen some in the first half of 2012, while the number of migrants returning to Mexico decreased, a report by U.S. and Mexican researchers said Tuesday.

It was the first time the net outflow of migrants from Mexico has increased since the 2007 economic slump caused a sharp drop in both migration and the amount of money sent home by Mexicans working in the U.S., as migrants found it harder to find work north of the border.

The report by Mexico’s Colegio de la Frontera Norte and the University of Southern California’s Tomas Rivera Policy Institute said the number of Mexican-born people in the United States seems to have stabilized at around 11.7 million and might grow slightly by year’s end. The number included Mexicans who migrated legally and those who crossed over illegally.

“The recession-induced decline of undocumented migration from Mexico appears to have stopped in the first half of 2012 amid tentative signs of a renewed northbound flow,” the study said.

The report is based on surveys done at Mexican border crossings, bus stations and airports and on U.S. deportation, repatriation and demographics data. It says heightened U.S. enforcement of immigration laws and state initiatives like one enacted in Arizona didn’t appear to have persuaded illegal migrants already in the United States to leave.

“Despite evidence of growing psychological effects on the migrants who are removed, the available data suggest that these efforts have failed to have substantial, ongoing effects on the size of the Mexican migrant population,” the report said. “On the contrary, fewer Mexican migrants have left the United States since those enforcement efforts went into effect.”