The distinction between bank and market based economies has a long tradition in applied macroeconomics. The two types differ not only in the level of financial activity channeled through the stock market and private banking, but also in their institutional frameworks. We challenge this traditional distinction between the two types of financial architecture. We develop an index that accounts for complementarity between financial markets and banking systems that has been hypothesized by Sylla (1998) and Song and Thakor (2010). The theoretical foundation of our empirical approach is the general equilibrium framework by Freixas and Rochet (1997). We validate the proposed index and the underlying theory of complementary using a random coefficient and a Generalized estimating equations (GEE).