What is our formal definition of market efficiency hypothesis (MEH)? A test of the MEH is a joint test of what two things? How does this limit our ability to test the MEH? How is it that market prices move in a "random walk" and yet are determined rationally? Market Efficiency Hypothesis (MEH): what are the differences between the following three forms of the MEH? What are the logical relations between the different forms? (i.e., do any of the forms imply another form? If so, which ones?) Weak Semi-strong strong What does the MEH not imply