"Damage Per Action" is the average damage dealt per action based on the amount of damage dealt times the chance to hit. The formula is:
DPA = Damage of Attack * chance to hit.
So, a Zombie with Vigour Mortis, Rend Flesh, and Death Grip would have a DPA of 1.5 with his hands. (3 points of damage * 50% to hit). This is useful in determining how much damage you can do in a certain number of rounds. For example if your Zombie has a DPS of 1.5 with his claws, and you have 10 actions left you can reasonably expect to do around 15 points of damage in that time. You can also make reasonable estimation about how much experience you will make through combat in a session, because 1 XP is gained per point of damage inflicted.
Please note that this calculation is fundamentally flawed as it is based on guns that never run out of ammunition, hence these damage per AP are ONLY valid for a person fully stocked up on guns and ammunition
A more correct calculation is being done as we speak that will include find rates averaged for ammunition (once you find your 12-20 guns you never drop them)
Infectious Bite is not included because its damage is based on actions by the infected, not the attacker. It also does not give experience. Digestion is not included because it doesn't affect damage dealt.
1Damage per AP never actually reaches 1.15. Rather, as AP used approaches infinite, Damage per AP approaches 1.15.
2Damage per AP never actually reaches 1.725. Rather, as AP used approaches infinite, Damage per AP approaches 1.725.