RE:RE:RE:CIBC Economics Not Bullish On Aerospace@ gas61di56 - The relevance is that stocks don't trade completely independent of their peer group. They usually trade in a range relative to the trading multiple of their peers for the simple fact that investors make comparisions between similar stocks. Buying a car would be an analogy. If you had a choice between a Ford and a Chev, you'd make your choice on the relative merit of one over the other based on the price between the two. Investors do the same thing with stocks. They compare them to other stocks engaged in the same business.
Further, many ETF's are structured to track a sector so if the aerospace sector, for example, is being bought or sold off, then it increases the tendancy for the underlying assets to trade in a range relative to their peers. In laymans terms, most house on a block will trade at more or less the same price and change in value more or less the same.