How efficient is extracting thc using alcohol?

I am making the "green dragon" and I was wondering how efficient is the alcohol at extracting the thc.
My other question is during the extraction process, does the thc get completely extracted from the plant matter? or is there an equilibrium distribution or ratio of thc between the plant matter and the alcohol?
My last question is in the case of equal ratio distribution, well another extraction process only yield half that concentration?