A number of recent papers have reported evidence that stock prices are more volatile than is consistent with efficient markets. We argue that the excess volatility tests address a definition of efficient markets that makes an extreme information assumption. We go on to test a weaker definition...

We investigate the performance of call markets at the open and close using a unique natural experiment provided by the London Stock Exchange where traders can choose between a call and an off-exchange dealership system. Although the call market dominates dealers in terms of price discovery, it...