In order to analyze the relationship between p2005 and y2005 contract prices, we can conclude whether there is a long-term stable cointegration relationship.
Thus, the relationship between p2005 and y2005 contract price is analyzed to draw the conclusion whether there is a long-term stable co-integration relationship.
Then it analyzes the relationship between P2005 and y2005 contract price, and concludes whether there is a long-term stable co integration relationship.