My paper is a DCC-Garch dynamic correlation analysis using industry stock indices upstream and downstream of the industry chain. Someone's comment: "if you measure the risks in the stock market, are there any common underlying factors that drive the real estate industry and its upstream and downstream industries? Without controlling these common factors, we might not be able to precisely quantify the risk spillover effect of real estate on upstream and downstream industries. Something needs to be done." I have read many papers that use this method without using control variables. Can you please advise which control variables can be used for this. Please advise! Thanks a lot!