How can damage be quantified in a game-agnostic way?

Question

We're all familiar with the usual pattern in games where players have "100 health", which is typically meant to represent an abstract percentage. Or, some games may use different numbers.

This bothers me because it's highly arbitrary. 100 whats? What are the units? This means that every weapon in the game needs to have another arbitrary quantity set on it for how much should be subtracted from the player's health when they are impacted by a bullet shot from a gun, a swing of a sword, etc.

However, there are some quantities that can be measured. A bullet's kinetic energy could be calculated using a formula such as 0.5 * mass * velocity * velocity. The question is then, how does this energy correspond to damage in the body?

Is there a way to quantify the damage to a human body? How can we measure the amount of trauma induced by a character being smacked with a hammer, or being sliced with a knife, or having bullets pass through their body? For the sake of keeping this simple, let's assume only regular-sized humans and assume that the body is a uniform mass of human-meat, changing the damage based on impact area (ex: headshots) can be separate from this quantifiable measurement of damage a weapon does to meat.

Answer 1

As outlined in a comment above, I'm inclined to agree with DavidT that trying to use one root balancing value across a diverse range of games is unlikely to be practical. Even when you allow for each game to adjust those values on import, the amount of one-off adjustment that would need to be made to fit well with the experience of each game is likely to outweigh the benefit of having a standardized input scale in the first place.

That said, if we had to pick some at least plausibly-principled basis for such an input scale, what's the best we could do?

I posed this question to a colleague who used to work in modelling and analyzing the impacts of weapons, explosives, crashes, etc. for the UK Ministry of Defence. They pointed me to Criteria for Incapacitating Soldiers with Fragments and Flechettes, a now-unclassified 1965 report by William Kokinakis and Joseph Sperrazza for the US military. My colleague described this as "the backbone of all military survivability/lethality analysis."

The full report is around 90 pages and too much to summarize well here. Its main approach to quantifying injury is to estimate a probability that a particular hit/wound will incapacitate a soldier, keeping them from performing some tactical role.

It includes formulae and parameter values to compute these probabilities from the projectile's mass and velocity, similar to the kinetic energy formula you gave, with varying degrees of complication depending on the scenario, part of body hit, clothing/armour worn, etc.

You may be able to use this probability as your standard measure of damage. When you need to compute a probability for a scenario not covered in this report, you can search for reports citing it that cover the scenario of interest to you: they should have what you need to convert answer into the same probability terms.

Exactly which number you use will involve some arbitrary choices (e.g. do you assume limb, body, or head shots, or some particular ratio of each? Do you assume a target who's nude, or armoured? At what range? Are they in an assault or defence role? etc...) so unfortunately you'll still have to put your thumb on the scale somewhere when boiling down something as complex as physics tearing through biology into a single number.

Since we ultimately need to make some arbitrary choices anyway, I'd argue in favour of making your arbitrary system as simple as possible. If you can pick a number for a weapon in a couple minutes instead of hours of research, and if a game developer importing your weapon can do so without having to read and understand a 90-page military statistics report, then your proposed system has a better chance of getting wider support. The more technical you make it, the harder it is to create content for or implement into a game. So the arbitrary-unit 0-100 scale has a certain appeal there.

Answer 2

I don't think it matters if the OP is developing a game themselves, or trying to generate a system/framework to be utilized by games.

In either case, I don't think it is practical to try to apply real world injuries/damage (in a realistic way) to a game context, for the following reasons:

1. Game Balance - in most games that have a health status, the amount of damage done by weapons, poison, fall damage etc. is a key lever used by the developer to encourage diversity of weapon usage and strategy. For example some games implement a damage fall off, which is unrealistic when compared to the relative damage from a real weapon at various ranges.
2. Timeline of effect - IRL some weapons and impact location are immediately disabling (instant kill) where as others can still be fatal, but not instantly so (not a doctor) but historically wounds to the lower torso were often fatal, however such wounds did not preclude returning fire for a short period of time. With some exceptions, someone being functional IRL for a minute or two probably doesn't have a huge effect on the overall battle, however given the compressed time lines of a game, it could be significant.
3. Real world factors - such as fear and pain would accompany a wound, in most cases they would impact the effectiveness of a real world combatant, however the affects are going to be difficult to simulate in a game (the player doesn't really fear for their life).

In summary, I don't think it is possible to create a "a game-agnostic asset standard", since every game will have both different needs and implementation constraints(**) for how damage should be applied in that game.

** - What the devs have time/choose to implement.