Actually, the manufacturers have been completely forthcoming with this information. It is stated clearly that the pill, as does birth control pills, prevents pregnancy by preventing ovulation, as well as causing changes in the uterine lining that prevent implantation. The manufacturers have never disputed that fact.
I am attempting to locate the actual study, as this article provides no information at all other than it was a mathematical model. The statistics used are also somewhat vague, as an effectiveness rate of 90% is much higher than those that I have seen for emergency contraception.
It may have what you’re looking for below:
The abstract can be found at:
http://www.fertstert.org/article/PIIS0015028206047327/abstra...