In testimony before the House Intelligence Committee on Tuesday, the head of the National Security Agency, Gen. Keith Alexander, said the government surveillance programs which have set off a national debate had helped prevent more than 50 terrorist “events” since Sept. 11, 2001.

Many Americans appear to accept that defense of the program as true, according to a survey conducted just days before the hearing. A majority (53%) think the government’s collection of telephone and internet data has helped prevent terrorist attacks, while 41% say it has not.

But while a majority agree the program has helped prevent terrorist attacks, the public is still split on its view of the surveillance programs: 48% approve of the collection of data and 47% do not.

In addition, Americans are divided over when the information that former government contractor Edward Snowden leaked about the surveillance efforts served or harmed the public interest. Just under half (49%) said the leaks served the public interest while 44 % said they harmed it. Read more

Bruce Drake  is a former senior editor at Pew Research Center.