A Nobel prize-winning economist, James Tobin (1918-2002) theorized that firms would continue to invest as long as the value of their shares exceeded the replacement cost of their assets. The ratio of the market value of a firm to the net replacement cost of the firm’s assets is known as “Tobin’s Q”. If q is greater than 1, then it should pay the firm to expand, as the profit it should expect to make from its assets (reflected in the share price) exceeds the cost of the assets. If Q is less than 1, the firm would be better off selling its assets, which are worth more than shareholders currently expect the firm to earn in profit by retaining them. Tobin also gave his name to the “Tobin tax”, a (so far unimplemented) proposal to reduce speculative cross-border flows of capital by levying a small tax on foreign exchange transactions.