According to a new survey by the Pew Research Center, people who use Facebook and Twitter are less likely to share their opinions of hot issues.

The study which was done in conjunction with Rutgers University challenges the view of social media as a vehicle for debate by suggesting that sites like Facebook and Twitter might actually encourage self-censorship. Researchers said they detect what they call “spiral of silence” phenomenon: Unless someone knows that their audience agrees, they are likely to avoid discussing anything controversial.

The survey was conducted shortly after Edward Snowden acknowledged leaking classified intelligence that exposed widespread government surveillance of Americans’ phone and eMail records.