This line of analysis looks promising, but the post leaves too many important questions unanswered, including: * How have mergers and acquisitions affected the

This line of analysis looks promising, but the post leaves too many important questions unanswered, including: * How have mergers and acquisitions affected the rate of churn in the S&P 500? It could very well be that S&P 500 companies are disappearing from the list at a faster rate because they're being merged into or acquired by other companies at a faster rate. * To what extent does the rate of churn in the S&P 500 reflect declines in specific sectors of the economy unrelated to software? For example, US manufacturing has faced challenging times for several decades, so one would expect to see this trend reflected in the list. * How did the inflating and bursting of the Housing Bubble impact the companies exposed to that industry in the S&P 500? For example, many home builders and mortgage lenders boomed during the bubble and then went bust when the bubble burst. How is that reflected in the data? * How did the growth in financial services as a percentage of GDP affect the index prior to the financial crisis? How about after the financial crisis? Think not just about Lehman Brothers's demise, but about all the formerly high-flying financial firms that went bust or whose size is considerably smaller today.