For instance, Geoffrey Caveney demonstrated that the median price-to-free-cash-flow (P/FCF) for the S&P 500 SPDR Trust ( SPY ) is roughly 35. Higher or lower valuations depend largely on things like key personnel, average account size, client retention, economies of scale and the growth rate. It's also true that negative rate monetary policy (adjusted for inflation) has been a tremendous tailwind for stock price appreciation, as have the corporate tax cuts.