How to balance skills in games

I am making a zombie game (do not flame), and need to add the following traits:
-Hit skill
-Health skill
-Speed skill

So I have tried my usual formula, where you need 2 of the skill’s values to add up to the last skill’s value, but it is not optimal. It works, but is not good enough. So what do you guys use? This is the first time the equation has not fit the game. Also, feel free to give suggestions to other skills.

I don’t think there is any standard formula on how to set values for a player’s attributes or skills so that they are balanced. Each game is a case-to-case basis wherein you take into consideration a lot of other factors so that your game ends up being well-balanced.

You’ll have to figure out what works best for your game. It may involve some trial and error, but I suggest playing around with the values, keep on playtesting, have others playtest your game then continually balance and re-balance until you find what’s right for your game.

Consider making some test cases and run them for a few rounds of combat. Better yet, make a few thousand tests cases and run them for a few million rounds.

Start from constraint. First make your enemies/obstacles neutral then expect how much % player will survive on this level.