Economics
One ratio tells a company whether it's cheaper to build a factory or buy a rival's
Tobin's Q divides a firm's market value by the replacement cost of its physical assets. A Q above one means the market values the company for more than rebuilding it would cost, so new investment makes sense; below one, buying an existing competitor is cheaper than building. James Tobin popularised the ratio in 1969 to link stock market prices to real investment decisions.