The roles of expected profitability, Tobin's Q and cash flow in econometric models of company investment

Evidence that cash flow has a significant effect on investment after controlling for Tobin's average Q has been interpreted as suggesting the importance of financing constraints. Recent work shows that the Q model may not be identified if there are `bubbles' in stock market valuations that are persistent and correlated with fundamental values. Cash flow may then provide additional information about expected profitability that is not captured by average Q. Using data on UK companies, we find severe measurement error in average Q. We find that cash flow becomes insignificant after controlling for expected profitability using analysts' earnings forecasts (I/B/E/S).