After making the graph to see correlation between CM & price of raw material. We found that most of impact to CM is price of Ethylene and EDC respectively.
We can see that in Oct'15 we will get the highest CM because price of Ethylene & EDC are cheaper than another month. Although both of price of finished product and
price of raw material will have impact to CM, but in my opinion price of raw material will have more impact to CM.