There are two topics I'm covering - "lethality" in wargames and how modifiers interact with them, and the "proper" use of modifiers (i.e. how much is too much), and the impact of both on gameplay and game balance.
I feel a few of my recent topics have a "teaching your grandma to suck eggs" vibe, but they may be useful to at least highlight how these factors interact, and to articulate aloud what most wargamers instinctively understand.
LethalityThis is the chance of killing an enemy soldier after all rolls are taken into account. Usually there is a "to hit" roll and a "to damage" or "saving" roll (sometimes both of the latter); other times hits eke away at a percentage of the units total hitpoints.
Example A1: LOTR
In LOTR, an average archer hits on a 4+ on d6 (50%) and then kills on a 5+ (33%). 33% of 50% (i.e. .33 x .50) is a 16.5% chance to kill. That's about average, perhaps a little low.
Example B1: Infinity the Game
For example, in Infinity a solider has an unmodified chance to hit of 12 in 20 (60%) and then an chance to kill of 10 in 20 - 50% - (presuming assault rifle and +2 armour). 50% of 60% is a 30% chance to kill - very high. Given the average assault rifle shoots 3 x - that's a 90% chance to kill an unprepared enemy - unbelievably lethal for a wargame. If the opponent can react and fires back (RoF 1) using similar stats (30% lethality) it's even more likely someone will die. Note - in addition many Infinity weapons (48"+) handily outrange LoTR bows (24") further emphasizing the shooting lethality.
Note in both cases I am rather simplistically ignoring modifiers like range bands and cover. We'll get to that.
These are a key way to "influence" players to act in a particular way - a carrot (positive modifiers that increase the chance of success) and the stick (negative modifiers that decrease the chance of success.)
As we're talking about wargames, this primarily involves shooting and melee, though it can extend to movement (though movement tends to be pretty formulaic i.e. 6" move, halve for bad going and is seldom as influential or interesting).
There are a few common ways modifiers work. e.g.
(a) reduce/increase the target number to beat/go under on a dice i.e. beat 4+ on d6 reduced to beat 5+ on d6.
(b) the flip side of (a) i.e. add or subtract a number from the dice against a fixed target number i.e. beat 4 on d6, or beat 4 on d6 -1
(c) increase/decrease dice size. Beat 4+ with a d8; reduced to beat 4+ on a d6, increased beat 4+ on d10.
(d) add or remove dice (usually tied to "bucket of dice" method) i.e. roll 4 d6s, each 4+ is a success. Reduced to rolling 3 d6s, each 4+ is a success.
This isn't an exhaustive list, but you get the idea. Negative modifiers make it harder to accomplish stuff (usually but not limited to killing your opponent); positive modifiers make it easier.
(Note: I know sometimes a "negative" -1 modifier is a "good" thing depending on the mechanics; but I'm using positive and negative in the sense of how it benefits the unit/mini carrying out the action)
Not all Modifiers are created equal
In a game like DBA or SoBH (which use a d6+stat vs d6+stat mechanic) the effect of +1 to a d6 is not the same as a -1. The -1 has a more powerful effect as reducing the number makes it easier for your opponent to double or triple your score (which is how actions are resolved).
In a more obvious example, a -1 and -2 modifier on 2d6 are not a linear progression like it would be on a d10; the -2 modifier is much more powerful; the modifiers themselves can vary significantly compared to the target number. I.e. if your target number is 7, a -1 modifier is not the same as a -1 modifier against a target number of 11. (Couldn't be bothered doing the exact math - I'm on holidays! - have a google if you are interested, i.e. like the example here).
Too many modifiers
There is a bit of a backlash against modifiers. This is because many of us were raised on games like WRG moderns which had a modifier for every situation, e.g.
Machine gun platoon had a bad night's sleep: -1 to hit rolls
Captain got a "Dear John" letter: -1 to his saving throw
Extra coffee ration: +1 RoF, +1" move
Too many modifiers means you can forget to use them. A bit like charts and tables, and stats (I've ranted on the latter before) there has been a bit of a backlash against modifiers and many games avoid them or limit them altogether - to the detriment of gamplay. Like how stats have been minimised, actually increasing the amount of rules to learn, and how movement has been needlessly simplified and homogenized to everyone moves 6" - it's one of those "throw the baby out with the bathwater" situations. Modifiers serve an important purpose, used sensibly.
Well, how many modifiers, then?
Well, what tactics and behaviours do you want to encourage?
If you really want your players to use their troops a certain way, encourage/discourage them with modifiers. So as many modifiers as behaviours you want to encourage/discourage.
If you had to back me into a corner, I'd say 3-6 or so is easy enough to remember. Infinity does a good job of this; modifiers strongly influence play, and it only uconsiders two - cover, and the range band of the weapon.
Lethality & Modifiers
Now modifiers are used to change the behaviour of players by making certain tactics more desirable. Let's consider the use of cover.
How useful is cover in LOTR? Well, it gives a 4+ on d6 save (50%) to the "to hit" of the shot; so when in cover, a bow's lethality is reduced from 16.5% to 8%.
So how useful is cover in Infinity? Well it imposes a -3 (15%) penalty to both the hit and the damage roll. So it becomes 45% to hit, with 35% to damage. In the end, it also halves the effect, dropping the lethality to 15%. Fired in a burst of 3 shots, 45% lethality is still comparatively high.
It halves the lethality in both games.... so cover is equally important and desirable in both?
No. Whilst the effect of cover is the same (halving the lethality) due to the 'absolute' lethality values of 90/45% vs 16/8% cover is far more important in Infinity. You must have cover for even a 50/50 chance to survive in Infinity. Whereas in LOTR you have a good chance (83%) of surviving a enemy archer's shot, even standing in the open.
Lethality strongly impacts gameplay, You can see how shooting in Infinity (45%+) is 500% more lethal than LOTR (8%) which makes sense - one is a modern/sci fi game dominated by automatic weapons where cover is paramount; the other a medieval fantasy where melee is supposed to be decisive - and the lethality levels and ratios regarding shooting means this is how they play out..
The high lethality of Infinity shooting (45%) has other effects besides making staying in cover very desirable. Due to the fact very few opponents survive long enough to close to melee range (as opposed to LOTR, where a unit could expect to survive 3-4 turns of enemy shooting while closing to melee range) melee stats and skills are proportionately less valuable. Presuming the shooting has equal range and you move the same distance (more on that later) you are 5x more likely to be killed before you get into melee - so melee stats are proportionately less useful.
I call this "opportunity" and it's important when balancing stats, skills and abilities. The key question is "how often can I be expected to use this stat/ability?" For example, you can expect to use movement every turn, and shooting most turns (depending on the range.) A magic spell that can only be deployed after killing a specific enemy hero might be less valuable as it can only rarely be utilized.
Opportunity is linked with many things, like the move:shoot ratio, e.g. if we wanted to make melee viable in an Infinity-like game, we could simply ramp up the lethality of melee. E.g. in modern PC shooters, a rifle takes 4-5 body shots to kill; a melee attack is an instant 1-shot kill. The melee attack is 4-5x more lethal, which balances the fact guns are effective at 4-5x longer ranges, making melee a viable option where it otherwise would not.
Lethality, Modifiers and Terrain
We see how cover can radically alter the lethality in both LOTR and Infinity. This underscores the importance of terrain and that devs need to make clear how much terrain is expected (like Infinity does) i.e. how much terrain was the game "balanced" against. Obviously, having more or less terrain than what the designer regards as "normal" will unbalance the value of missile and melee units, for instance. I.e. I typically have very crowded boards, with lots of terrain. Far more than the 'average' GW layout. As a result, in my LOTR games, goblins tend to beat elves rather handily. This is because the elves superior bows are rendered less effective than on a 'traditional' board and and increases the value of goblin's movement modifier (that freely enables them to move up/over obstacles without penalty). As you can see, terrain type/density messes up the balance of the points system.
Range Bands, like terrain, this another factor to consider. LOTR rather simplistically has only one range band - shooting is as effective at 24" as at 1" - missing out on a layer of tactics. Infinity has multiple 8" bands - a shot at close range (0-8") might have a +15% modifier and one at extreme range a -30% to hit modifier which significantly impacts the lethality. This adds depth to gameplay as you want to be in the best range for your weapon - be it short (handgun or shotgun) or long (sniper rifle). Interestingly, heavy or unwieldy weapons (like sniper rifles or LMGs) attract negative -15% modifiers at close ranges. Combined with +15% or +30% boosts to close quarters weapons; and a sniper rifle might be at a combined 45% disadvantage to a shotgun in close quarters.
As you can see, by significantly altering the success chance of an action, modifiers can be used to by the game designer to "guide" tactics.
Lethality, m:s, and Points Systems
Logically, it seems to me this is a good place to start as any when designing points systems to balance a game. Take LOTR, which is a relatively simple, familiar game.
We know a bow has a 16.5% lethality, and it works out to 18"(? forgot precise range)
A melee weapon has similar lethality (16.5%) and works to 0" but you can move 6" per turn.
So... bows seem 3 x more valuable than melee weapons due to the m1:3s ratio. (Interestingly, the ratio of bows/melee only troops is capped at 1:3 when making an army)
Since boosting your Defence from 5 to 6 by +1 would drop lethality to 8% to both bows and melee. This means Defence perhaps twice as valuable(?) as boosting the lethality of your melee weapon or bow. However going from defence 4 to 5 goes from 25% lethality to 16.5% lethality; whilst it offers a similar 8% jump in protection, is not proportionately as valuable. I.e. going from Defence 4 to 5 improves defence by 50%; going from 5 to 6 doubles it (100%).
Anyway, that's just a quick example of how lethality and m:s can be used as a math-based basis for point systems - whilst also showing there is a lot to consider.
Disclaimer: I write this on the balcony of an apartment at Tin Can Bay, so my math might be a bit dodgy - the ocean view (and my 2 year old) are a bit distracting to my ADHD*... However the "theory" is sound enough. So what was that again?
*Alleged by my wife; not clinically proven
Here's the main "thrust" of this post, for those who got lost amidst the wall of text:
Lethality can influence gameplay (both relative/ratio and as an absolute)
Modifiers can influence player behaviour (tactics) in making certain actions more/less desirable
Modifiers are not all equal; a -1 can vary in significance due to differing dice mechanisms
Modifiers, lethality and m:s ratios are important to game balance; they can form a useful basis when designing a points system
Modifiers are important and very useful when kept within sensible boundaries
"Opportunity" is how often a stat or ability can be used
Many factors such as terrain can impact game balance and mess up your points system (but we aren't naive enough to think points systems can actually be balanced, anyway)
Again, this may be a bit of a "duh that's obvious" post, but it may be handy in "breaking down" rules so when designing we can articulate deliberately what we understand or "get" instinctively.