where Q'it is industry-adjusted Q (firm Q minus industry-median Q), Xit is a vector of governance variables (G, its components, or inclusion in one of the extreme portfolios) and Wit is a vector of firm characteristics. As elements of W, we follow Shin and Stulz
[2000] and include the log of the book value of assets and the log of firm age as of December of year t.18 Daines [2001] found that Q is different for Delaware and non-Delaware firms, so we also include a Delaware dummy in W. Morck and Yang [2001] show
that S&P 500 inclusion has a positive impact on Q, and that this impact increased during the 1990s; thus, we also include a dummy variable for S&P 500 inclusion in W.