We show that product differentiation reduces the informativeness of a firm’s stock price (or its peers’ stock prices) about the value of its growth opportunities. This results in less efficient exercise of a firm’s growth options when managers rely on information in stock prices for their decisions. This informational cost of differentiation induces conformity in product market strategies and is larger for private firms. Hence, a firm should differentiate more after going public. We confirm this prediction empirically and show that the post-IPO increase in differentiation is stronger for firms with better informed managers or less informative peers’ stock prices.Received January 19, 2016; editorial decision May 8, 2018 by Editor Itay Goldstein.

Firms significantly reduce their investment in response to nonfundamental drops in the stock price of their product-market peers. We argue that this results stems from managers’ limited ability to filter out the noise in the stock prices when using them as signals about their investment opportunities. Ensuing losses of capital investment and shareholders’ wealth are economically large and even affect firms not facing severe financing constraints or agency problems. Our findings offer a novel perspective on how stock market inefficiencies can affect the real economy, even in the absence of financing or agency frictions.Received December 14, 2016; editorial decision July 30, 2018 by Editor Itay Goldstein.