Screaming will likely cause the attacker to try to shut you up. Use your imagination.
Someone who puts you in a situation where you need to scream, should be shot. Whether the attacker lives or dies from a bullet is the gamble he took. Have you ever really heard a real scream? Listen to those 911 calls on Youtube that I posted. Those are not movie and tv screams from actors, thay are real disturbing noises that humans make when they are about to be killed/raped/mamed.