On the Evolution of Trading Institutions: The Platform Design Paradox

This paper analyzes a learning model where sophisticated market designers create new trading platforms and boundedly rational traders select among them. We ask wether "Walrasian'''' platforms, leading to efficient (market - clearing) trading outcomes, will dominate the market in the long run. If several market designers are competing, we find that traders will learn to select non-market clearing platforms with prices systematically above the market-clearing level, provided at least one such platform is introduced by a market designer. This in turn leads all market designers to introduce such inefficient (non-market clearing) platforms. Hence platform competition induces non-competitive market outcomes.