Assistance Factor (AF) is a feature on ASC that encourages you to help your teammates. AF confers you a bonus at the start of each map. The bonus increases the number of points each Special Infected is worth.
Whenever you heal, revive, or defibrillate your teammates during each chapter of the campaign, you gain one additional point for your next Special Infected until the end of the chapter. The bonus resets to your base AF value at the beginning of next map.
How do you increase your Assistance Factor? Here is a quick run down:
Then, this is divided by 4*B
Finally, the quotient is divided by 2.
X = number of times you heal/defibrillate teammates with medkits and defibrillators
Y = number of times you heal yourself
I = number of times you help someone from incapacitation
K = number of times you give adrenaline to someone
J = number of times you give pills to someone
B = number of times you incapacitated someone
This will be your AF. It is the number of bonus points you would get for killing a Special Infected at the start of every chapter. The bonus point rounds up. For example, if your AF is 3.5, you will receive 4 extra points for each Special you kill.
In order to be eligible for the bonus, you have to meet the following criteria:
Have 10,000 points
Have a minimum of 24 hours of playtime on ASC.
You can find out your AF by visiting your personal statistics page on ASC website or by typing !factor or !rank in-game. You can also see the leaderboard for AF by typing the !assist command.