Bond vs stock market's Q: Testing for stability across frequencies and over time

In this paper we revisit the evidence recently provided by Philippon (2009) about the relationship among bond market's Q, stock market's Q and aggregate investments for the US. Specifically, we analyze the stability of the relationship between aggregate investment and the two measures of Q across frequencies and over time. We find that the relationship between aggregate investment and stock market's Q, in contrast to that with bond market's Q, is both frequency-dependent and time-varying. Both the successfulness of bond market's Q and the poor performance of the usual Tobin's Q can be explained by taking into account stability across frequencies of the first and instability over time of the latter.