To White17, sorry for the typo. It's 17%, not 27%. It is quoted from 888options as from CBOE (see my comment above). It is a good news to hear someone from real world about the low chance of early exercise. In my opinion, you didn't get any early assignment as a daily trader is because you are a daily trader and don't keep the options with deep ITM. As a non-daily trader and strategy model trader, I can't be able to monitor my account daily and my be invovled in deep ITM options with negative extrinsic value which would be easier to get early exercise by arbitrageur if someone sells it on open option market. You might be able to close the position easily as a daily trader. But it is hard for me and my strategy model does not allow it.
To Spreadgod, your analysis matches exactly what I am thinking. Thanks for your input because I was worrying about if there is any miscalculation in my analysis. Yes, the early exercise is a gift if it has premium and I handle it myself or have enough margin. It may be a problem if it does not have premium and I don't have enough margin.
After earlier assignment, if my long option goes deeper ITM, my position does not change or closes. But if my long option goes shallower ITM, my position becomes better because of the extrinsic value of the long. And if my long position goes OTM, oh boy, I becomes the BIG WINNER and big thanks to the early exerciser.
I am going to use a strategy model to trade the options. The strategy model is more complicated than a single spread as in my above sample. I have to buy and sell a lot of times with several different kinds of spreads. I can't quit a spread when it is exercised becuase it hurts the other spreads as well. I haven't had a chance to look how bad it is if I close a spread in the moddle because of an early assignment. To me the solution would be (from best to worst):
1> Rebuild the spread if the short option has premium. It is unlikly to happen in real world. Everyone is too smart to do so.

2> Keep the assignment with more than enough margin when the short option does not have premium. I may get extra from the long extrinsic. It can't be rebuild because there are too many arbitrageurs there. Cons: Never screwed up with margin or you are screwed.
3> Close the spread. I should give a suggestion to brokers to bring it as a feature when a spread is created. The choice 1 is another good feature for a spread too. Trader will love it. Will you? Cons: You have to be quick than your borker.
4> Close the assignment. It is most brokers' action if there is no enough margin. This leaves the ITM long option at risk. You may gain more if the long goes deeper ITM and you may lose money if the long goes shallower ITM.
Most brokers require 30% of the stock values if early assignment happens while most option price is only a fraction of the stock price. The choice for me might be only 1> and 3>.
Is there anyone trading options with a model? I don't think I am the first one to do so on this board.
Happy reading. I am going to find where I can get more margin.
