It does not really matter if the CBOE trades the majority of equity options or not, it is assumed that the same trend would exist in other trading exchanges as well. The CBOE simply provides half hourly reading to get a handle on the situation during the day. An EPC of .65 is still very high, and since my model has historically used the CBOE (where I can easily go and check historical data), it is best to continues with it. The recent string of extremely high EPC is almost unprecedented. One can try and rationalize it "away" at own own risk. The question is how represenative is the CBOE of all options trading, until I find that on other exchanges the EPC is drastically different, I see no reason to worry about the "purity" of these data.