Financial economics is the branch of economics studying the interrelation of financial variables, such as prices, interest rates and shares, as opposed to those concerning the real economy. Financial economics concentrates on influences of real economic variables on financial ones, in contrast to pure finance. It centres on decision making under uncertainty in the context of the financial markets, and the resultant economic and financial models. It essentially explores how rational investors would apply decision theory to the problem of investment. Here, the twin assumptions of rationality and market efficiency lead to modern portfolio theory (the CAPM), and to the Black–Scholes theory for option valuation; it further studies phenomena and models where these assumptions do not hold, or are extended. “Financial economics”, at least formally, also considers investment under “certainty” (Fisher separation theorem, “theory of investment value”, Modigliani-Miller theorem) and hence also contributes to corporate finance theory. Financial Econometrics is the branch of Financial Economics that uses econometric techniques to parameterize the relationships suggested.
Although closely related, the disciplines of economics and finance are distinctive. The “economy” is a social institution that organizes a society’s production, distribution, and consumption of goods and services,” all of which must be financed.
Economists make a number of abstract assumptions for purposes of their analyses and predictions. They generally regard financial markets that function for the financial system as an efficient mechanism. Instead, financial markets are subject to human error and emotion. New research discloses the mischaracterization of investment safety and measures of financial products and markets so complex that their effects, especially under conditions of uncertainty, are impossible to predict. The study of finance is subsumed under economics as financial economics, but the scope, speed, power relations and practices of the financial system can uplift or cripple whole economies and the well-being of households, businesses and governing bodies within them—sometimes in a single day.