The Misuse of Tobin's Q

50 Pages Posted: 15 Feb 2018 Last revised: 28 Jun 2018

See all articles by Robert P. Bartlett

Robert P. Bartlett

University of California, Berkeley - School of Law; University of California, Berkeley - Berkeley Center for Law, Business and the Economy

Frank Partnoy

University of California, Berkeley - School of Law

Date Written: February 4, 2018

Abstract

We examine the common and growing misuse of Tobin’s q as a proxy for firm value within the law and finance literatures. We trace the history of Tobin’s q, beginning with its original role as a mean-reverting construct that macroeconomists used to model investment policy. We document how the original version of q morphed into the simplified market-to-book ratio version that law and finance scholars regularly use today to examine regulatory policy, corporate governance, and other economic phenomena. Whereas macroeconomists rejected this simplistic version of q because of measurement error problems, law and finance scholars embraced it as a proxy for firm value.

In addition, we demonstrate empirically why the simplistic version of q is so problematic. Many of the problems arise because regressions that have as their dependent variable a ratio with book value in the denominator are likely to produce biased estimates, due to both omitted assets and time-varying, firm-specific characteristics that can systematically alter a firm’s book value. As a result, the simplistic version of q produces non-classical measurement error in regression specifications that seek to estimate the relationship between firm value and various corporate and regulatory phenomena. We also confirm, consistent with macroeconomists’ view of the original Tobin’s q, that the market-to-book estimate of q is mean-reverting in terms of stockholder returns.

Finally, we suggest a new approach. We replicate the details of one leading study that was based on the simplistic version of q and then show how its results differ when we employ several alternative approaches. We propose that scholars should use these alternative approaches, including direct estimates of firm value instead of the simplistic market-to-book ratio, and, when possible, should supplement the popular fixed effects estimator with the first difference estimator. Overall, our message is straightforward: scholars should view with suspicion any assertions about corporate governance and regulation that are based on the use of market-to-book ratios as the dependent variable in regressions.

Keywords: Tobin's q, firm value, corporate governance, law and finance

JEL Classification: C58, G30, G34, K22

Suggested Citation

Bartlett, Robert P. and Partnoy, Frank, The Misuse of Tobin's Q (February 4, 2018). UC Berkeley Public Law Research Paper. Available at SSRN: https://ssrn.com/abstract=3118020 or http://dx.doi.org/10.2139/ssrn.3118020

Robert P. Bartlett (Contact Author)

University of California, Berkeley - School of Law ( email )

215 Boalt Hall
Berkeley, CA 94720-7200
United States
510-642-6646 (Phone)

University of California, Berkeley - Berkeley Center for Law, Business and the Economy

UC Berkeley School of Law
Berkeley, CA 94720

Frank Partnoy

University of California, Berkeley - School of Law ( email )

215 Boalt Hall
Berkeley, CA 94720-7200
United States

Register to save articles to
your library

Register

Paper statistics

Downloads
613
rank
39,712
Abstract Views
1,980
PlumX