I've got several friends in law enforcement. According to them, because of incidents around the country they've had to have tactical training for dealing with a knife wielding attacker. A knife wielding attacker can close and stab a standing officer before he can draw and fire his service weapon at about 10 yards. If we are talking about a novice with a gun and a novice with a knife, then lethality for both men are going to drop significantly beyond that range. Don't underestimate a knife; I've had several skilled people from many backgrounds say it is the scariest thing you will ever face.