*Originally posted by GunFlavoured*

From what I understand it assumes that every player has perfect calling and pushing ranges

*Originally posted by Anssi*

ICM expects your opponents to play perfectly.

Not really. ICM doesn't assume or expect anything. You are mixing up several different things.

ICM is a model which does the following: it takes the chipstacks and the payout structure and tells you how much every chipstack is worth in $ (if you have any math background, then the simpliest way to put it is that ICM is a function).

In the following I will assume that ICM is actualy a correct way to calculate the value of your chipstack*.

Now we have a Nash equilibrium which is a concept from game theory and it is a strategy (strategy for all players, not just 1 of them). Nash equilibrium is such a strategy, that no player can improve his expected value if he changes his individual strategy from the Nash equilibrium and others don't change theirs (he can hurt other players, he can give them better EV, he can hurt himself, but he will never get a better 'deal' for himself unless other players deviate from the Nash equilibrium as well).

If you take these 2 concepts, you can calculate the 'Nash ranges', which is a Nash equilibrium strategy for all players. Tools like ICM Trainer use ICM to find the Nash ranges (the ICM is used to calculate $equity of your stack if you fold, if you call and win, if you call and loose).

I hope I made it clear, it's a bit complicated stuff for people who don't study/work with game theory.

Now I feel I can answer you other questions and possibly the answer is clear from what I written already.

*Originally posted by GunFlavoured*

I want to know if I should be following the ICM model

Yes, you should be following the ICM under the assumtion that ICM calculates the $equity correctly (there are exception, see *).

But no, you should not be following the Nash ranges charts, if your opponents don't do it. You can get better results by adjusting to them. Get ICM wizzard or similar tool, or just use simple rule: if they call too tight, you can push looser (because they won't call anyway), if they call loosely, you push tight (because they will call and you need to win the showdown). If they push tight, don't call (obvious).

*Originally posted by GunFlavoured*

Does this mean that the ICM hards are now -EV or are they still +EV but maybe not as much.

The Nash ranges are 0 EV if everyone uses them.

If your opponents don't play accordingly and you do, you will be +EV in the long run, but some hands might be -EV (you and your opponent both loose equity and the players not in the hand gain). If you have a strong read on some villains, you should follow it and adapt your play.

* - In reality ICM is pretty good and it gives results which are close to the real value in most cases, but it's not perfect. Under some extreme conditions it can actually be way off.

Take this example: We have a double or nothing SNG, where 5 players are paid $100. There are 6 players left and 1 players has all the chips in the game except 5. The other 5 players have 1 chip each and you are one of these players.

Now ICM will tell you that your 1 chip is worth $80 (because the bigstack 'always' wins and 4 out of the other 5 people win and it's random who will be the unlucky guy).

But if you are actually in the big blind and the bigstack is in the small blind the next hand, you are forced to go all-in vs. him and there is 50 % chance of you busting.

Therefore the real value of your chip is a little less than $50.

The are other situations where ICM fails, there are better ways to calculate your $equity, but they are pretty complicated, so they aren't used in practise.