Financial innovation

There are several interpretations of the phrase financial innovation. In general, it refers to the creating and marketing of new types of securities.

Economic theory has much to say about what types of securities should exist, and why some may not exist (why some markets should be "incomplete") but little to say about why new types of securities should come into existence.

One interpretation of the Modigliani-Miller theorem is that taxes and regulation are the only reasons for investors to care what kinds of securities firms issue, whether debt, equity, or something else. The theorem states that the structure of a firm's liabilities should have no bearing on its net worth (absent taxes, etc.). The securities may trade at different prices depending on their composition, but they must ultimately add up to the same value.

Furthermore, there should be little demand for specific types of securities. The capital asset pricing model, first developed by Jack L. Treynor and William F. Sharpe, suggests that investors should fully diversify and their portfolios should be a mixture of the "market" and a risk-free investment. Investors with different risk/return goals can use leverage to increase the ratio of the market return to the risk-free return in their portfolios. However, Richard Roll argued that this model was incorrect, because investors cannot invest in the entire market. This implies there should be demand for instruments that open up new types of investment opportunities (since this gets investors closer to being able to buy the entire market), but not for instruments that merely repackage existing risks (since investors already have as much exposure to those risks in their portfolio).

If the world existed as the Arrow-Debreu model posits, then there would be no need for financial innovation. The Arrow-Debreu model assumes that investors are able to purchase securities that pay off if and only if a certain state of the world occurs. Investors can then combine these securities to create portfolios that have whatever payoff they desire. The fundamental theorem of finance states that the price of assembling such a portfolio will be equal to its expected value under the appropriate risk-neutral measure.

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